### 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
gui_base->add_child(project_settings_editor);
	scene_import_settings = memnew(SceneImportSettings);
	gui_base->add_child(scene_import_settings);
	audio_stream_import_settings = memnew(AudioStreamImportSettings);
	gui_base->add_child(audio_stream_import_settings);
	fontdata_import_settings = memnew(DynamicFontImportSettings);
	gui_base->add_child(fontdata_import_settings);
	export_template_manager = memnew(ExportTemplateManager);
	gui_base->add_child(export_template_manager);
	feature_profile_manager = memnew(EditorFeatureProfileManager);
	gui_base->add_child(feature_profile_manager);
	build_profile_manager = memnew(EditorBuildProfileManager);
	gui_base->add_child(build_profile_manager);
	about = memnew(EditorAbout);
	gui_base->add_child(about);
	feature_profile_manager->connect("current_feature_profile_changed", callable_mp(this, &EditorNode::_feature_profile_changed));
#if !defined(ANDROID_ENABLED) && !defined(WEB_ENABLED)
	fbx_importer_manager = memnew(FBXImporterManager);
	gui_base->add_child(fbx_importer_manager);
#endif
	warning = memnew(AcceptDialog);
	warning->set_unparent_when_invisible(true);
	warning->add_button(TTR("Copy Text"), true, "copy");
	warning->connect("custom_action", callable_mp(this, &EditorNode::_copy_warning));
	ED_SHORTCUT("editor/next_tab", TTR("Next Scene Tab"), KeyModifierMask::CMD_OR_CTRL + Key::TAB);
	ED_SHORTCUT("editor/prev_tab", TTR("Previous Scene Tab"), KeyModifierMask::CMD_OR_CTRL + KeyModifierMask::SHIFT + Key::TAB);
	ED_SHORTCUT("editor/filter_files", TTR("Focus FileSystem Filter"), KeyModifierMask::CMD_OR_CTRL + KeyModifierMask::ALT + Key::P);
	command_palette = EditorCommandPalette::get_singleton();
	command_palette->set_title(TTR("Command Palette"));
	gui_base->add_child(command_palette);