### Godot version

v4.2.dev.custom_build [0c2144da9]

### System information

Debian Linux X11 Xfce

### Issue description

Prerequisite: Be in Single Window Mode in the Editor
The Filesystem Dock is unusable when it is floating, which is not expected.
It appears garbled in the top-left corner:
![image](https://github.com/godotengine/godot/assets/6299227/109f7922-97de-44c3-814a-ca7f970e0602)

The following errors are shown:
```
  editor/window_wrapper.cpp:220 - Condition "!is_window_available()" is true.
  editor/window_wrapper.cpp:202 - Condition "!get_window_enabled()" is true. Returning: Rect2i()
  editor/window_wrapper.cpp:207 - Condition "!get_window_enabled()" is true. Returning: -1
  editor/window_wrapper.cpp:207 - Condition "!get_window_enabled()" is true. Returning: -1
```

bisecting lead to #62378
possibly related to #44439

### Steps to reproduce

1. Start a project in the Editor
2. Switch to Single Window Mode in the Editor and reload (if necessary)
3. Make the Filesystem Dock floating

### Minimal reproduction project

Editor issue
Ref<InputEventMouse> me = p_input;
	if (me.is_valid()) {
		Vector2 point = me->get_position();
		int nrect = -1;
		for (int i = 0; i < DOCK_SLOT_MAX; i++) {
			if (dock_select_rect[i].has_point(point)) {
				nrect = i;
				break;
			}
		}
		if (nrect != dock_select_rect_over_idx) {
			dock_select->queue_redraw();
			dock_select_rect_over_idx = nrect;
		}
		if (nrect == -1) {