### 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
switch (p_what) {
		case NOTIFICATION_PROCESS: {
			if (opening_prev && !confirmation->is_visible()) {
				opening_prev = false;
			}
			bool global_unsaved = EditorUndoRedoManager::get_singleton()->is_history_unsaved(EditorUndoRedoManager::GLOBAL_HISTORY);
			bool scene_or_global_unsaved = global_unsaved || EditorUndoRedoManager::get_singleton()->is_history_unsaved(editor_data.get_current_edited_scene_history_id());
			if (unsaved_cache != scene_or_global_unsaved) {
				unsaved_cache = scene_or_global_unsaved;
				_update_title();
			}
			if (editor_data.is_scene_changed(-1)) {
				_update_scene_tabs();
			}
			
			uint64_t frame = Engine::get_singleton()->get_frames_drawn();
			uint64_t tick = OS::get_singleton()->get_ticks_msec();
			if (frame != update_spinner_step_frame && (tick - update_spinner_step_msec) > (1000 / 8)) {
				update_spinner_step++;