### Godot version

v4.0 rc6

### System information

Windows 10

### Issue description

When using a ViewportTexture from a SubViewport on a TextureRect, it throws errors after running the scene once and then switching scenes in the editor.
![Pasted image 20230227212626](https://user-images.githubusercontent.com/44676282/221680047-984fa03e-33d1-4856-9a7f-1700b28423cf.png)


### Steps to reproduce

Run the canvas-scene once.
Switch to another scene in the editor.
Switch back to the canvas-scene

### Minimal reproduction project

[ViewportTextureError.zip](https://github.com/godotengine/godot/files/10844099/ViewportTextureError.zip)

cpos = c->get_transform().xform(cpos);
					if (cursor_shape != Control::CURSOR_ARROW) {
						break;
					}
					if (c->data.mouse_filter == Control::MOUSE_FILTER_STOP) {
						break;
					}
					if (c->is_set_as_top_level()) {
						break;
					}
					c = c->get_parent_control();
				}
			}
			ds_cursor_shape = (DisplayServer::CursorShape)cursor_shape;
			bool stopped = over->can_process() && _gui_call_input(over, mm);
			if (stopped) {
				set_input_as_handled();
			}
		}
		if (gui.dragging) {
			
			Control *drag_preview = _gui_get_drag_preview();
			if (drag_preview) {
				drag_preview->set_position(mpos);
			}
			gui.drag_mouse_over = over;
			gui.drag_mouse_over_pos = Vector2();
			
			
			Viewport *embedder = nullptr;