Fix MeshInstance2D rect

(cherry picked from commit 1a347e9cf37480b5b87f331c4c41c6fa60db5132)

scene/2d/mesh_instance_2d.cpp

@@ -96,6 +96,10 @@ Rect2 MeshInstance2D::_edit_get_rect() const {
 
 	return Node2D::_edit_get_rect();
 }
+
+bool MeshInstance2D::_edit_use_rect() const {
+	return mesh.is_valid();
+}
 #endif
 
 MeshInstance2D::MeshInstance2D() {

scene/2d/mesh_instance_2d.h

@@ -48,6 +48,7 @@ protected:
 public:
 #ifdef TOOLS_ENABLED
 	virtual Rect2 _edit_get_rect() const;
+	virtual bool _edit_use_rect() const;
 #endif
 
 	void set_mesh(const Ref<Mesh> &p_mesh);