### 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<ResourceImporterTexture> import_texture;
		import_texture.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_texture);
		Ref<ResourceImporterLayeredTexture> import_cubemap;
		import_cubemap.instantiate();
		import_cubemap->set_mode(ResourceImporterLayeredTexture::MODE_CUBEMAP);
		ResourceFormatImporter::get_singleton()->add_importer(import_cubemap);
		Ref<ResourceImporterLayeredTexture> import_array;
		import_array.instantiate();
		import_array->set_mode(ResourceImporterLayeredTexture::MODE_2D_ARRAY);
		ResourceFormatImporter::get_singleton()->add_importer(import_array);
		Ref<ResourceImporterLayeredTexture> import_cubemap_array;
		import_cubemap_array.instantiate();
		import_cubemap_array->set_mode(ResourceImporterLayeredTexture::MODE_CUBEMAP_ARRAY);
		ResourceFormatImporter::get_singleton()->add_importer(import_cubemap_array);
		Ref<ResourceImporterLayeredTexture> import_3d;
		import_3d.instantiate();
		import_3d->set_mode(ResourceImporterLayeredTexture::MODE_3D);
		ResourceFormatImporter::get_singleton()->add_importer(import_3d);
		Ref<ResourceImporterImage> import_image;
		import_image.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_image);
		Ref<ResourceImporterTextureAtlas> import_texture_atlas;
		import_texture_atlas.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_texture_atlas);
		Ref<ResourceImporterDynamicFont> import_font_data_dynamic;
		import_font_data_dynamic.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_font_data_dynamic);