### 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)

stopped = _gui_call_input(over, drag_event);
			}
			if (stopped) {
				set_input_as_handled();
			}
			return;
		}
	}
	if (mm.is_null() && mb.is_null() && p_event->is_action_type()) {
		if (gui.dragging && p_event->is_action_pressed("ui_cancel") && Input::get_singleton()->is_action_just_pressed("ui_cancel")) {
			_perform_drop();
			set_input_as_handled();
			return;
		}
		if (p_event->is_action_pressed("ui_cancel")) {
			
			_gui_cancel_tooltip();
			if (gui.tooltip_popup) {
				
				
				
				set_input_as_handled();
				return;
			}
		}
		if (gui.key_focus && !gui.key_focus->is_visible_in_tree()) {
			gui.key_focus->release_focus();
		}
		if (gui.key_focus) {
			gui.key_event_accepted = false;