### 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
_save_scene_with_preview(p_file);
				project_run_bar->play_main_scene((bool)pick_main_scene->get_meta("from_native", false));
			}
		} break;
		case FILE_EXPORT_MESH_LIBRARY: {
			Ref<MeshLibrary> ml;
			if (file_export_lib_merge->is_pressed() && FileAccess::exists(p_file)) {
				ml = ResourceLoader::load(p_file, "MeshLibrary");
				if (ml.is_null()) {
					show_accept(TTR("Can't load MeshLibrary for merging!"), TTR("OK"));
					return;
				}
			}
			if (ml.is_null()) {
				ml = Ref<MeshLibrary>(memnew(MeshLibrary));
			}
			MeshLibraryEditor::update_library_file(editor_data.get_edited_scene_root(), ml, true, file_export_lib_apply_xforms->is_pressed());
			Error err = ResourceSaver::save(ml, p_file);
			if (err) {
				show_accept(TTR("Error saving MeshLibrary!"), TTR("OK"));
				return;
			} else if (ResourceCache::has(p_file)) {
				
				ResourceLoader::load(p_file)->reload_from_file();
			}
		} break;
		case RESOURCE_SAVE:
		case RESOURCE_SAVE_AS: {
			ERR_FAIL_COND(saving_resource.is_null());
			save_resource_in_path(saving_resource, p_file);