### 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
help_menu->set_item_icon(help_menu->get_item_index(HELP_QA), gui_base->get_theme_icon(SNAME("ExternalLink"), SNAME("EditorIcons")));
			help_menu->set_item_icon(help_menu->get_item_index(HELP_REPORT_A_BUG), gui_base->get_theme_icon(SNAME("ExternalLink"), SNAME("EditorIcons")));
			help_menu->set_item_icon(help_menu->get_item_index(HELP_COPY_SYSTEM_INFO), gui_base->get_theme_icon(SNAME("ActionCopy"), SNAME("EditorIcons")));
			help_menu->set_item_icon(help_menu->get_item_index(HELP_SUGGEST_A_FEATURE), gui_base->get_theme_icon(SNAME("ExternalLink"), SNAME("EditorIcons")));
			help_menu->set_item_icon(help_menu->get_item_index(HELP_SEND_DOCS_FEEDBACK), gui_base->get_theme_icon(SNAME("ExternalLink"), SNAME("EditorIcons")));
			help_menu->set_item_icon(help_menu->get_item_index(HELP_COMMUNITY), gui_base->get_theme_icon(SNAME("ExternalLink"), SNAME("EditorIcons")));
			help_menu->set_item_icon(help_menu->get_item_index(HELP_ABOUT), gui_base->get_theme_icon(SNAME("Godot"), SNAME("EditorIcons")));
			help_menu->set_item_icon(help_menu->get_item_index(HELP_SUPPORT_GODOT_DEVELOPMENT), gui_base->get_theme_icon(SNAME("Heart"), SNAME("EditorIcons")));
			for (int i = 0; i < main_editor_buttons.size(); i++) {
				main_editor_buttons.write[i]->add_theme_font_override("font", gui_base->get_theme_font(SNAME("main_button_font"), SNAME("EditorFonts")));
				main_editor_buttons.write[i]->add_theme_font_size_override("font_size", gui_base->get_theme_font_size(SNAME("main_button_font_size"), SNAME("EditorFonts")));
			}
			HashSet<String> updated_textfile_extensions;
			bool extensions_match = true;
			const Vector<String> textfile_ext = ((String)(EDITOR_GET("docks/filesystem/textfile_extensions"))).split(",", false);
			for (const String &E : textfile_ext) {
				updated_textfile_extensions.insert(E);
				if (extensions_match && !textfile_extensions.has(E)) {
					extensions_match = false;
				}
			}
			if (!extensions_match || updated_textfile_extensions.size() < textfile_extensions.size()) {
				textfile_extensions = updated_textfile_extensions;
				EditorFileSystem::get_singleton()->scan();
			}
			_update_update_spinner();
		} break;
	}
}
void EditorNode::_update_update_spinner() {