### 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
EditorFileDialog::set_default_display_mode((EditorFileDialog::DisplayMode)EDITOR_GET("filesystem/file_dialog/display_mode").operator int());
			bool theme_changed =
					EditorSettings::get_singleton()->check_changed_settings_in_group("interface/theme") ||
					EditorSettings::get_singleton()->check_changed_settings_in_group("interface/editor/font") ||
					EditorSettings::get_singleton()->check_changed_settings_in_group("interface/editor/main_font") ||
					EditorSettings::get_singleton()->check_changed_settings_in_group("interface/editor/code_font") ||
					EditorSettings::get_singleton()->check_changed_settings_in_group("text_editor/theme") ||
					EditorSettings::get_singleton()->check_changed_settings_in_group("text_editor/help/help") ||
					EditorSettings::get_singleton()->check_changed_settings_in_group("filesystem/file_dialog/thumbnail_size") ||
					EditorSettings::get_singleton()->check_changed_settings_in_group("run/output/font_size") ||
					EditorSettings::get_singleton()->check_changed_settings_in_group("interface/touchscreen/increase_scrollbar_touch_area") ||
					EditorSettings::get_singleton()->check_changed_settings_in_group("interface/touchscreen/scale_gizmo_handles");
			if (theme_changed) {
				theme = create_custom_theme(theme_base->get_theme());
				DisplayServer::set_early_window_clear_color_override(true, theme->get_color(SNAME("background"), SNAME("Editor")));
				theme_base->set_theme(theme);
				gui_base->set_theme(theme);
				get_window()->set_theme(theme);
				gui_base->add_theme_style_override("panel", gui_base->get_theme_stylebox(SNAME("Background"), SNAME("EditorStyles")));
				main_vbox->set_anchors_and_offsets_preset(Control::PRESET_FULL_RECT, Control::PRESET_MODE_MINSIZE, gui_base->get_theme_constant(SNAME("window_border_margin"), SNAME("Editor")));
				main_vbox->add_theme_constant_override("separation", gui_base->get_theme_constant(SNAME("top_bar_separation"), SNAME("Editor")));
				scene_root_parent->add_theme_style_override("panel", gui_base->get_theme_stylebox(SNAME("Content"), SNAME("EditorStyles")));
				bottom_panel->add_theme_style_override("panel", gui_base->get_theme_stylebox(SNAME("BottomPanel"), SNAME("EditorStyles")));
				tabbar_panel->add_theme_style_override("panel", gui_base->get_theme_stylebox(SNAME("tabbar_background"), SNAME("TabContainer")));
				scene_tabs->add_theme_constant_override("icon_max_width", gui_base->get_theme_constant(SNAME("class_icon_size"), SNAME("Editor")));
				scene_tab_add_ph->set_custom_minimum_size(scene_tab_add->get_minimum_size());
				main_menu->add_theme_style_override("hover", gui_base->get_theme_stylebox(SNAME("MenuHover"), SNAME("EditorStyles")));
			}
			scene_tabs->set_max_tab_width(int(EDITOR_GET("interface/scene_tabs/maximum_width")) * EDSCALE);
			_update_scene_tabs();