Fix GLES directional shadow uninitialized data

Valgrind shows directional_shadow.fbo accessed when uninitialized in directional_shadow_create.

drivers/gles2/rasterizer_scene_gles2.h

@@ -288,13 +288,13 @@ public:
 	bool shadow_atlas_update_light(RID p_atlas, RID p_light_intance, float p_coverage, uint64_t p_light_version);
 
 	struct DirectionalShadow {
-		GLuint fbo;
-		GLuint depth;
-		GLuint color;
+		GLuint fbo = 0;
+		GLuint depth = 0;
+		GLuint color = 0;
 
-		int light_count;
-		int size;
-		int current_light;
+		int light_count = 0;
+		int size = 0;
+		int current_light = 0;
 	} directional_shadow;
 
 	virtual int get_directional_light_shadow_size(RID p_light_intance);

drivers/gles3/rasterizer_scene_gles3.h

@@ -278,11 +278,11 @@ public:
 	bool shadow_atlas_update_light(RID p_atlas, RID p_light_intance, float p_coverage, uint64_t p_light_version);
 
 	struct DirectionalShadow {
-		GLuint fbo;
-		GLuint depth;
-		int light_count;
-		int size;
-		int current_light;
+		GLuint fbo = 0;
+		GLuint depth = 0;
+		int light_count = 0;
+		int size = 0;
+		int current_light = 0;
 	} directional_shadow;
 
 	virtual int get_directional_light_shadow_size(RID p_light_intance);