### 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<ResourceImporterBMFont> import_font_data_bmfont;
		import_font_data_bmfont.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_font_data_bmfont);
		Ref<ResourceImporterImageFont> import_font_data_image;
		import_font_data_image.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_font_data_image);
		Ref<ResourceImporterCSVTranslation> import_csv_translation;
		import_csv_translation.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_csv_translation);
		Ref<ResourceImporterWAV> import_wav;
		import_wav.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_wav);
		Ref<ResourceImporterOBJ> import_obj;
		import_obj.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_obj);
		Ref<ResourceImporterShaderFile> import_shader_file;
		import_shader_file.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_shader_file);
		Ref<ResourceImporterScene> import_scene;
		import_scene.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_scene);
		Ref<ResourceImporterScene> import_animation;
		import_animation = Ref<ResourceImporterScene>(memnew(ResourceImporterScene(true)));
		ResourceFormatImporter::get_singleton()->add_importer(import_animation);
		{
			Ref<EditorSceneFormatImporterCollada> import_collada;
			import_collada.instantiate();
			ResourceImporterScene::add_importer(import_collada);
			Ref<EditorOBJImporter> import_obj2;
			import_obj2.instantiate();