Fix more "may be used initialized" warnings from GCC 7

Fixes the following GCC 7 warnings:
```
core/cowdata.h:269:47: warning: 'alloc_size' may be used uninitialized in this function [-Wmaybe-uninitialized]
core/error_macros.h:163:26: warning: 'nearest_point' may be used uninitialized in this function [-Wmaybe-uninitialized]
core/image.cpp:1579:5: warning: 'colormap_size' may be used uninitialized in this function [-Wmaybe-uninitialized]
core/image.cpp:1582:12: warning: 'size_height' may be used uninitialized in this function [-Wmaybe-uninitialized]
core/image.cpp:1590:23: warning: 'size_width' may be used uninitialized in this function [-Wmaybe-uninitialized]
core/image.cpp:1599:29: warning: 'pixel_size' may be used uninitialized in this function [-Wmaybe-uninitialized]
core/math/face3.cpp:207:15: warning: 'tri_max' may be used uninitialized in this function [-Wmaybe-uninitialized]
core/math/face3.cpp:209:15: warning: 'tri_min' may be used uninitialized in this function [-Wmaybe-uninitialized]
drivers/gles3/rasterizer_scene_gles3.cpp:665:22: warning: 'best_used_frame' may be used uninitialized in this function [-Wmaybe-uninitialized]
drivers/gles3/rasterizer_storage_gles3.cpp:865:27: warning: 'blit_target' may be used uninitialized in this function [-Wmaybe-uninitialized]
drivers/gles3/rasterizer_storage_gles3.cpp:980:29: warning: 'blit_target' may be used uninitialized in this function [-Wmaybe-uninitialized]
drivers/gles3/shader_gles3.h:122:9: warning: '<anonymous>.ShaderGLES3::Version::frag_id' may be used uninitialized in this function [-Wmaybe-uninitialized]
drivers/gles3/shader_gles3.h:122:9: warning: '<anonymous>.ShaderGLES3::Version::id' may be used uninitialized in this function [-Wmaybe-uninitialized]
drivers/gles3/shader_gles3.h:122:9: warning: '<anonymous>.ShaderGLES3::Version::vert_id' may be used uninitialized in this function [-Wmaybe-uninitialized]
editor/plugins/script_editor_plugin.cpp:1980:31: warning: 'se' may be used uninitialized in this function [-Wmaybe-uninitialized]
editor/scene_tree_dock.cpp:840:30: warning: 'new_node' may be used uninitialized in this function [-Wmaybe-uninitialized]
editor/spatial_editor_gizmos.cpp:4259:9: warning: 'a1' may be used uninitialized in this function [-Wmaybe-uninitialized]
editor/spatial_editor_gizmos.cpp:4259:9: warning: 'lll' may be used uninitialized in this function [-Wmaybe-uninitialized]
editor/spatial_editor_gizmos.cpp:4259:9: warning: 'lul' may be used uninitialized in this function [-Wmaybe-uninitialized]
editor/spatial_editor_gizmos.cpp:4260:9: warning: 'a2' may be used uninitialized in this function [-Wmaybe-uninitialized]
editor/spatial_editor_gizmos.cpp:4261:9: warning: 'a3' may be used uninitialized in this function [-Wmaybe-uninitialized]
editor/spatial_editor_gizmos.cpp:4265:3: warning: 'enable_lin' may be used uninitialized in this function [-Wmaybe-uninitialized]
editor/spatial_editor_gizmos.cpp:4294:3: warning: 'enable_ang' may be used uninitialized in this function [-Wmaybe-uninitialized]
editor/spatial_editor_gizmos.cpp:4311:34: warning: 'll' may be used uninitialized in this function [-Wmaybe-uninitialized]
editor/spatial_editor_gizmos.cpp:4311:34: warning: 'ul' may be used uninitialized in this function [-Wmaybe-uninitialized]
scene/3d/voxel_light_baker.cpp:1655:47: warning: 'cone_dirs' may be used uninitialized in this function [-Wmaybe-uninitialized]
scene/3d/voxel_light_baker.cpp:1656:73: warning: 'cone_weights' may be used uninitialized in this function [-Wmaybe-uninitialized]
scene/gui/texture_progress.cpp:181:6: warning: 'cp' may be used uninitialized in this function [-Wmaybe-uninitialized]
scene/gui/texture_progress.cpp:181:6: warning: 'cq' may be used uninitialized in this function [-Wmaybe-uninitialized]
servers/physics/shape_sw.cpp:1056:19: warning: 'support_max' may be used uninitialized in this function [-Wmaybe-uninitialized]
```

3 files changed, 12 insertions, 17 deletions

diff --git a/editor/plugins/script_editor_plugin.cpp b/editor/plugins/script_editor_plugin.cpp
index 7cda15bdc6..d26e1a39f6 100644
--- a/editor/plugins/script_editor_plugin.cpp
+++ b/editor/plugins/script_editor_plugin.cpp
@@ -1960,7 +1960,7 @@ bool ScriptEditor::edit(const RES &p_resource, int p_line, int p_col, bool p_gra
 
 	// doesn't have it, make a new one
 
-	ScriptEditorBase *se;
+	ScriptEditorBase *se = NULL;
 
 	for (int i = script_editor_func_count - 1; i >= 0; i--) {
 		se = script_editor_funcs[i](p_resource);
diff --git a/editor/scene_tree_dock.cpp b/editor/scene_tree_dock.cpp
index 08f1ece2d4..a6a014f3bd 100644
--- a/editor/scene_tree_dock.cpp
+++ b/editor/scene_tree_dock.cpp
@@ -797,7 +797,7 @@ void SceneTreeDock::_tool_selected(int p_tool, bool p_confirm_override) {
 		case TOOL_CREATE_USER_INTERFACE:
 		case TOOL_CREATE_FAVORITE: {
 
-			Node *new_node;
+			Node *new_node = NULL;
 
 			if (TOOL_CREATE_FAVORITE == p_tool) {
 				String name = selected_favorite_root.get_slicec(' ', 0);
diff --git a/editor/spatial_editor_gizmos.cpp b/editor/spatial_editor_gizmos.cpp
index 96bca86f83..a321cb16c5 100644
--- a/editor/spatial_editor_gizmos.cpp
+++ b/editor/spatial_editor_gizmos.cpp
@@ -4201,21 +4201,16 @@ void JointSpatialGizmoPlugin::CreateGeneric6DOFJointGizmo(
 	float cs = 0.25;
 
 	for (int ax = 0; ax < 3; ax++) {
-		/*r_points.push_back(p_offset.translated(Vector3(+cs,0,0)).origin);
-		r_points.push_back(p_offset.translated(Vector3(-cs,0,0)).origin);
-		r_points.push_back(p_offset.translated(Vector3(0,+cs,0)).origin);
-		r_points.push_back(p_offset.translated(Vector3(0,-cs,0)).origin);
-		r_points.push_back(p_offset.translated(Vector3(0,0,+cs*2)).origin);
-		r_points.push_back(p_offset.translated(Vector3(0,0,-cs*2)).origin); */
-
-		float ll;
-		float ul;
-		float lll;
-		float lul;
-
-		int a1, a2, a3;
-		bool enable_ang;
-		bool enable_lin;
+		float ll = 0;
+		float ul = 0;
+		float lll = 0;
+		float lul = 0;
+
+		int a1 = 0;
+		int a2 = 0;
+		int a3 = 0;
+		bool enable_ang = false;
+		bool enable_lin = false;
 
 		switch (ax) {
 			case 0: