### 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 (!unsaved_status.is_empty()) {
							if (p_option == RELOAD_CURRENT_PROJECT) {
								save_confirmation->set_ok_button_text(TTR("Save & Reload"));
								save_confirmation->set_text(unsaved_status);
							} else {
								save_confirmation->set_ok_button_text(TTR("Save & Quit"));
								save_confirmation->set_text(unsaved_status);
							}
							save_confirmation->reset_size();
							save_confirmation->popup_centered();
							plugin_to_save = editor_data.get_editor_plugin(i);
							break;
						}
					}
					if (plugin_to_save) {
						break;
					}
					_discard_changes();
					break;
				}
				if (save_each) {
					tab_closing_menu_option = current_menu_option;
					for (int i = 0; i < editor_data.get_edited_scene_count(); i++) {
						tabs_to_close.push_back(editor_data.get_scene_path(i));
					}
					_proceed_closing_scene_tabs();
				} else {
					String unsaved_scenes;
					int i = _next_unsaved_scene(true, 0);
					while (i != -1) {