### 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
project_menu->add_child(vcs_actions_menu);
	project_menu->set_item_submenu(project_menu->get_item_index(VCS_MENU), "Version Control");
	add_editor_plugin(memnew(AudioBusesEditorPlugin(audio_bus_editor)));
	for (int i = 0; i < EditorPlugins::get_plugin_count(); i++) {
		add_editor_plugin(EditorPlugins::create(i));
	}
	for (const StringName &extension_class_name : GDExtensionEditorPlugins::get_extension_classes()) {
		add_extension_editor_plugin(extension_class_name);
	}
	GDExtensionEditorPlugins::editor_node_add_plugin = &EditorNode::add_extension_editor_plugin;
	GDExtensionEditorPlugins::editor_node_remove_plugin = &EditorNode::remove_extension_editor_plugin;
	for (int i = 0; i < plugin_init_callback_count; i++) {
		plugin_init_callbacks[i]();
	}
	resource_preview->add_preview_generator(Ref<EditorTexturePreviewPlugin>(memnew(EditorTexturePreviewPlugin)));
	resource_preview->add_preview_generator(Ref<EditorImagePreviewPlugin>(memnew(EditorImagePreviewPlugin)));
	resource_preview->add_preview_generator(Ref<EditorPackedScenePreviewPlugin>(memnew(EditorPackedScenePreviewPlugin)));
	resource_preview->add_preview_generator(Ref<EditorMaterialPreviewPlugin>(memnew(EditorMaterialPreviewPlugin)));
	resource_preview->add_preview_generator(Ref<EditorScriptPreviewPlugin>(memnew(EditorScriptPreviewPlugin)));
	resource_preview->add_preview_generator(Ref<EditorAudioStreamPreviewPlugin>(memnew(EditorAudioStreamPreviewPlugin)));
	resource_preview->add_preview_generator(Ref<EditorMeshPreviewPlugin>(memnew(EditorMeshPreviewPlugin)));
	resource_preview->add_preview_generator(Ref<EditorBitmapPreviewPlugin>(memnew(EditorBitmapPreviewPlugin)));
	resource_preview->add_preview_generator(Ref<EditorFontPreviewPlugin>(memnew(EditorFontPreviewPlugin)));
	resource_preview->add_preview_generator(Ref<EditorGradientPreviewPlugin>(memnew(EditorGradientPreviewPlugin)));
	{
		Ref<StandardMaterial3DConversionPlugin> spatial_mat_convert;
		spatial_mat_convert.instantiate();
		resource_conversion_plugins.push_back(spatial_mat_convert);
		Ref<ORMMaterial3DConversionPlugin> orm_mat_convert;
		orm_mat_convert.instantiate();