Unbind the framebuffer when updating meshes.

While the vertex shaders used to update the meshes aren't actually rendering to the framebuffer, they may still refuse to run with some framebuffers bound - such as XR with multiple views.

(cherry picked from commit 679f5bf410)

drivers/gles3/storage/mesh_storage.cpp

@@ -1075,6 +1075,7 @@ void MeshStorage::update_mesh_instances() {
 	}
 
 	glEnable(GL_RASTERIZER_DISCARD);
+	glBindFramebuffer(GL_FRAMEBUFFER, 0);
 	// Process skeletons and blend shapes using transform feedback
 	while (dirty_mesh_instance_arrays.first()) {
 		MeshInstance *mi = dirty_mesh_instance_arrays.first()->self();