### 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)

}
				gui.currently_dragged_subwindow->_rect_changed_callback(new_rect);
				if (DisplayServer::get_singleton()->has_feature(DisplayServer::FEATURE_CURSOR_SHAPE)) {
					DisplayServer::get_singleton()->cursor_set_shape(DisplayServer::CURSOR_MOVE);
				}
			}
			if (gui.subwindow_drag == SUB_WINDOW_DRAG_CLOSE) {
				gui.subwindow_drag_close_inside = gui.subwindow_drag_close_rect.has_point(mm->get_position());
			}
			if (gui.subwindow_drag == SUB_WINDOW_DRAG_RESIZE) {
				Vector2i diff = mm->get_position() - gui.subwindow_drag_from;
				Size2i min_size = gui.currently_dragged_subwindow->get_min_size();
				Size2i min_size_clamped = gui.currently_dragged_subwindow->get_clamped_minimum_size();
				min_size_clamped.x = MAX(min_size_clamped.x, 1);
				min_size_clamped.y = MAX(min_size_clamped.y, 1);
				Rect2i r = gui.subwindow_resize_from_rect;
				Size2i limit = r.size - min_size_clamped;
				switch (gui.subwindow_resize_mode) {
					case SUB_WINDOW_RESIZE_TOP_LEFT: {
						diff.x = MIN(diff.x, limit.x);
						diff.y = MIN(diff.y, limit.y);
						r.position += diff;
						r.size -= diff;
					} break;
					case SUB_WINDOW_RESIZE_TOP: {
						diff.x = 0;
						diff.y = MIN(diff.y, limit.y);
						r.position += diff;
						r.size -= diff;
					} break;