### 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
singleton->file_dialogs.insert(p_dialog);
}
void EditorNode::_file_dialog_unregister(FileDialog *p_dialog) {
	singleton->file_dialogs.erase(p_dialog);
}
void EditorNode::_editor_file_dialog_register(EditorFileDialog *p_dialog) {
	singleton->editor_file_dialogs.insert(p_dialog);
}
void EditorNode::_editor_file_dialog_unregister(EditorFileDialog *p_dialog) {
	singleton->editor_file_dialogs.erase(p_dialog);
}
Vector<EditorNodeInitCallback> EditorNode::_init_callbacks;
void EditorNode::_begin_first_scan() {
	OS::get_singleton()->benchmark_begin_measure("editor_scan_and_import");
	EditorFileSystem::get_singleton()->scan();
}
Error EditorNode::export_preset(const String &p_preset, const String &p_path, bool p_debug, bool p_pack_only) {
	export_defer.preset = p_preset;
	export_defer.path = p_path;
	export_defer.debug = p_debug;
	export_defer.pack_only = p_pack_only;
	cmdline_export_mode = true;
	return OK;
}
void EditorNode::show_accept(const String &p_text, const String &p_title) {