OpenGL: fix culling without depth prepass

This commit ensures a known backface culling state when rendering, even
if no depth prepass is used. This fixes backside culling not being
applied properly in some situations, most notably in scenes that only
use backside culling on mobile platforms.

drivers/gles3/rasterizer_scene_gles3.cpp

@@ -1895,6 +1895,10 @@ void RasterizerSceneGLES3::render_scene(const Ref<RenderSceneBuffers> &p_render_
 	glBindFramebuffer(GL_FRAMEBUFFER, rt->fbo);
 	glViewport(0, 0, rb->width, rb->height);
 
+	glCullFace(GL_BACK);
+	glEnable(GL_CULL_FACE);
+	scene_state.cull_mode = GLES3::SceneShaderData::CULL_BACK;
+
 	// Do depth prepass if it's explicitly enabled
 	bool use_depth_prepass = config->use_depth_prepass;
 
@@ -1910,9 +1914,6 @@ void RasterizerSceneGLES3::render_scene(const Ref<RenderSceneBuffers> &p_render_
 		glEnable(GL_DEPTH_TEST);
 		glDepthFunc(GL_LEQUAL);
 		glDisable(GL_SCISSOR_TEST);
-		glCullFace(GL_BACK);
-		glEnable(GL_CULL_FACE);
-		scene_state.cull_mode = GLES3::SceneShaderData::CULL_BACK;
 
 		glColorMask(0, 0, 0, 0);
 		glClearDepth(1.0f);