### 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
dock_slot[DOCK_SLOT_LEFT_UR]->set_tab_title(dock_slot[DOCK_SLOT_LEFT_UR]->get_tab_idx_from_control(SceneTreeDock::get_singleton()), TTR("Scene"));
	
	dock_slot[DOCK_SLOT_LEFT_UR]->add_child(ImportDock::get_singleton());
	dock_slot[DOCK_SLOT_LEFT_UR]->set_tab_title(dock_slot[DOCK_SLOT_LEFT_UR]->get_tab_idx_from_control(ImportDock::get_singleton()), TTR("Import"));
	
	dock_slot[DOCK_SLOT_LEFT_BR]->add_child(FileSystemDock::get_singleton());
	dock_slot[DOCK_SLOT_LEFT_BR]->set_tab_title(dock_slot[DOCK_SLOT_LEFT_BR]->get_tab_idx_from_control(FileSystemDock::get_singleton()), TTR("FileSystem"));
	
	dock_slot[DOCK_SLOT_RIGHT_UL]->add_child(InspectorDock::get_singleton());
	dock_slot[DOCK_SLOT_RIGHT_UL]->set_tab_title(dock_slot[DOCK_SLOT_RIGHT_UL]->get_tab_idx_from_control(InspectorDock::get_singleton()), TTR("Inspector"));
	
	dock_slot[DOCK_SLOT_RIGHT_UL]->add_child(NodeDock::get_singleton());
	dock_slot[DOCK_SLOT_RIGHT_UL]->set_tab_title(dock_slot[DOCK_SLOT_RIGHT_UL]->get_tab_idx_from_control(NodeDock::get_singleton()), TTR("Node"));
	
	dock_slot[DOCK_SLOT_RIGHT_UL]->add_child(history_dock);
	dock_slot[DOCK_SLOT_RIGHT_UL]->set_tab_title(dock_slot[DOCK_SLOT_RIGHT_UL]->get_tab_idx_from_control(history_dock), TTR("History"));
	
	dock_slot[DOCK_SLOT_LEFT_UL]->hide();
	dock_slot[DOCK_SLOT_LEFT_BL]->hide();
	dock_slot[DOCK_SLOT_RIGHT_BL]->hide();
	dock_slot[DOCK_SLOT_RIGHT_UR]->hide();
	dock_slot[DOCK_SLOT_RIGHT_BR]->hide();
	left_l_vsplit->hide();
	right_r_vsplit->hide();
	
	left_r_hsplit->set_split_offset(270 * EDSCALE);
	main_hsplit->set_split_offset(-270 * EDSCALE);
	
	const String docks_section = "docks";
	default_layout.instantiate();