### 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
if (waiting_for_first_scan) {
		waiting_for_first_scan = false;
		OS::get_singleton()->benchmark_end_measure("editor_scan_and_import");
		
		
		RenderingServer::get_singleton()->global_shader_parameters_load_settings(true);
		
		if (!singleton->cmdline_export_mode) {
			EditorResourcePreview::get_singleton()->start();
		}
		_load_editor_layout();
		if (!defer_load_scene.is_empty()) {
			OS::get_singleton()->benchmark_begin_measure("editor_load_scene");
			load_scene(defer_load_scene);
			defer_load_scene = "";
			OS::get_singleton()->benchmark_end_measure("editor_load_scene");
			OS::get_singleton()->benchmark_dump();
		}
	}
}
void EditorNode::_scan_external_changes() {