### 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
ProjectSettings::get_singleton()->setup(ProjectSettings::get_singleton()->get_resource_path(), String(), true);
	settings_changed = true;
}
void EditorNode::_vp_resized() {
}
void EditorNode::_titlebar_resized() {
	DisplayServer::get_singleton()->window_set_window_buttons_offset(Vector2i(title_bar->get_global_position().y + title_bar->get_size().y / 2, title_bar->get_global_position().y + title_bar->get_size().y / 2), DisplayServer::MAIN_WINDOW_ID);
	const Vector3i &margin = DisplayServer::get_singleton()->window_get_safe_title_margins(DisplayServer::MAIN_WINDOW_ID);
	if (left_menu_spacer) {
		int w = (gui_base->is_layout_rtl()) ? margin.y : margin.x;
		left_menu_spacer->set_custom_minimum_size(Size2(w, 0));
	}
	if (right_menu_spacer) {
		int w = (gui_base->is_layout_rtl()) ? margin.x : margin.y;
		right_menu_spacer->set_custom_minimum_size(Size2(w, 0));
	}
	if (title_bar) {
		title_bar->set_custom_minimum_size(Size2(0, margin.z - title_bar->get_global_position().y));
	}
}
void EditorNode::_version_button_pressed() {
	DisplayServer::get_singleton()->clipboard_set(version_btn->get_meta(META_TEXT_TO_COPY));
}
void EditorNode::_update_undo_redo_allowed() {
	EditorUndoRedoManager *undo_redo = EditorUndoRedoManager::get_singleton();
	file_menu->set_item_disabled(file_menu->get_item_index(EDIT_UNDO), !undo_redo->has_undo());
	file_menu->set_item_disabled(file_menu->get_item_index(EDIT_REDO), !undo_redo->has_redo());
}
void EditorNode::_node_renamed() {