### 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
#include "editor_node.h"
#include "core/config/project_settings.h"
#include "core/input/input.h"
#include "core/io/config_file.h"
#include "core/io/file_access.h"
#include "core/io/resource_loader.h"
#include "core/io/resource_saver.h"
#include "core/object/class_db.h"
#include "core/object/message_queue.h"
#include "core/os/keyboard.h"
#include "core/os/os.h"
#include "core/os/time.h"
#include "core/string/print_string.h"
#include "core/string/translation.h"
#include "core/version.h"
#include "main/main.h"
#include "scene/gui/color_picker.h"
#include "scene/gui/dialogs.h"
#include "scene/gui/file_dialog.h"