### Godot version

4.0.3-stable

### System information

Windows 10

### Issue description

In some projects ViewportTexture remains pink and doesn't render viewport content after upgrading from 4.0.2-stable to 4.0.3-stable. If a pair of files viewport.h/viewport.cpp are downgraded back to what they were in 4.0.2-stable, problem goes away.

This is how it looks in 4.0.3-stable:
![4 0 3_stable_viewport_4 0 3](https://github.com/godotengine/godot/assets/1449921/44c191a9-4b67-4b02-90b6-4ab615f62a73)

And this is how it looks if viewport.h/viewport.cpp are downgraded back to what they were in 4.0.2-stable.
![4 0 3_stable_viewport_4 0 2](https://github.com/godotengine/godot/assets/1449921/f5abc605-f129-4222-9c0e-e9a07621dd9d)



### Steps to reproduce

Unfortunately, I cannot come up wit a simple demo project reproducing the problem. It exists in some projects and doesn't exist in others.


### Minimal reproduction project

Cannot produce a simple project reproducing the problem. In simple projects it works fine.
if (gui.subwindow_drag != SUB_WINDOW_DRAG_DISABLED) {
		ERR_FAIL_COND_V(gui.currently_dragged_subwindow == nullptr, false);
		Ref<InputEventMouseButton> mb = p_event;
		if (mb.is_valid() && !mb->is_pressed() && mb->get_button_index() == MouseButton::LEFT) {
			if (gui.subwindow_drag == SUB_WINDOW_DRAG_CLOSE) {
				if (gui.subwindow_drag_close_rect.has_point(mb->get_position())) {
					
					gui.currently_dragged_subwindow->_event_callback(DisplayServer::WINDOW_EVENT_CLOSE_REQUEST);
				}
			}
			gui.subwindow_drag = SUB_WINDOW_DRAG_DISABLED;
			if (gui.currently_dragged_subwindow != nullptr) { 
				_sub_window_update(gui.currently_dragged_subwindow);
				gui.currently_dragged_subwindow = nullptr;
			}
		}
		Ref<InputEventMouseMotion> mm = p_event;