### 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
}
		} else {
			
			
			
			Ref<EditorFeatureProfile> profile = feature_profile_manager->get_current_profile();
			if (!profile.is_valid() || !profile->is_feature_disabled(EditorFeatureProfile::FEATURE_3D)) {
				img = Node3DEditor::get_singleton()->get_editor_viewport(0)->get_viewport_node()->get_texture()->get_image();
			}
		}
		if (img.is_valid() && img->get_width() > 0 && img->get_height() > 0) {
			img = img->duplicate();
			save.step(TTR("Creating Thumbnail"), 2);
			save.step(TTR("Creating Thumbnail"), 3);
			int preview_size = EDITOR_GET("filesystem/file_dialog/thumbnail_size");
			preview_size *= EDSCALE;
			
			int vp_size = MIN(img->get_width(), img->get_height());
			int x = (img->get_width() - vp_size) / 2;
			int y = (img->get_height() - vp_size) / 2;
			if (vp_size < preview_size) {
				
				img->crop_from_point(x, y, vp_size, vp_size);
			} else {
				int ratio = vp_size / preview_size;
				int size = preview_size * MAX(1, ratio / 2);
				x = (img->get_width() - size) / 2;
				y = (img->get_height() - size) / 2;
				img->crop_from_point(x, y, size, size);
				img->resize(preview_size, preview_size, Image::INTERPOLATE_LANCZOS);