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]
```

2 files changed, 8 insertions, 8 deletions

diff --git a/scene/gui/gradient_edit.cpp b/scene/gui/gradient_edit.cpp
index 19ffe681ef..934b84ec0c 100644
--- a/scene/gui/gradient_edit.cpp
+++ b/scene/gui/gradient_edit.cpp
@@ -238,21 +238,21 @@ void GradientEdit::_gui_input(const Ref<InputEvent> &p_event) {
 		if (mm->get_shift()) {
 			float snap_treshhold = 0.03;
 			float smallest_ofs = snap_treshhold;
-			bool founded = false;
-			int nearest_point;
+			bool found = false;
+			int nearest_point = 0;
 			for (int i = 0; i < points.size(); ++i) {
 				if (i != grabbed) {
 					float temp_ofs = ABS(points[i].offset - newofs);
 					if (temp_ofs < smallest_ofs) {
 						smallest_ofs = temp_ofs;
 						nearest_point = i;
-						if (founded)
+						if (found)
 							break;
-						founded = true;
+						found = true;
 					}
 				}
 			}
-			if (founded) {
+			if (found) {
 				if (points[nearest_point].offset < newofs)
 					newofs = points[nearest_point].offset + 0.00001;
 				else
diff --git a/scene/gui/texture_progress.cpp b/scene/gui/texture_progress.cpp
index 7ecdccb0e4..75f88dc4e6 100644
--- a/scene/gui/texture_progress.cpp
+++ b/scene/gui/texture_progress.cpp
@@ -148,9 +148,9 @@ Point2 TextureProgress::unit_val_to_uv(float val) {
 	float angle = (val * Math_TAU) - Math_PI * 0.5;
 	Point2 dir = Vector2(Math::cos(angle), Math::sin(angle));
 	float t1 = 1.0;
-	float cp;
-	float cq;
-	float cr;
+	float cp = 0;
+	float cq = 0;
+	float cr = 0;
 	float edgeLeft = 0.0;
 	float edgeRight = 1.0;
 	float edgeBottom = 0.0;