### 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
ERR_FAIL_COND(p_event.is_null());
	Ref<InputEventKey> k = p_event;
	if ((k.is_valid() && k->is_pressed() && !k->is_echo()) || Object::cast_to<InputEventShortcut>(*p_event)) {
		EditorPlugin *old_editor = editor_plugin_screen;
		if (ED_IS_SHORTCUT("editor/next_tab", p_event)) {
			int next_tab = editor_data.get_edited_scene() + 1;
			next_tab %= editor_data.get_edited_scene_count();
			_scene_tab_changed(next_tab);
		}
		if (ED_IS_SHORTCUT("editor/prev_tab", p_event)) {
			int next_tab = editor_data.get_edited_scene() - 1;
			next_tab = next_tab >= 0 ? next_tab : editor_data.get_edited_scene_count() - 1;
			_scene_tab_changed(next_tab);
		}
		if (ED_IS_SHORTCUT("editor/filter_files", p_event)) {
			FileSystemDock::get_singleton()->focus_on_filter();
		}
		if (ED_IS_SHORTCUT("editor/editor_2d", p_event)) {
			editor_select(EDITOR_2D);
		} else if (ED_IS_SHORTCUT("editor/editor_3d", p_event)) {
			editor_select(EDITOR_3D);
		} else if (ED_IS_SHORTCUT("editor/editor_script", p_event)) {
			editor_select(EDITOR_SCRIPT);
		} else if (ED_IS_SHORTCUT("editor/editor_help", p_event)) {
			emit_signal(SNAME("request_help_search"), "");
		} else if (ED_IS_SHORTCUT("editor/editor_assetlib", p_event) && AssetLibraryEditorPlugin::is_available()) {
			editor_select(EDITOR_ASSETLIB);
		} else if (ED_IS_SHORTCUT("editor/editor_next", p_event)) {
			_editor_select_next();