### 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
recent_scenes->reset_size();
			
			if (EditorDebuggerNode::get_singleton()->is_visible()) {
				bottom_panel->add_theme_style_override("panel", gui_base->get_theme_stylebox(SNAME("BottomPanelDebuggerOverride"), SNAME("EditorStyles")));
			}
			
			for (int i = 0; i < singleton->main_editor_buttons.size(); i++) {
				Button *tb = singleton->main_editor_buttons[i];
				EditorPlugin *p_editor = singleton->editor_table[i];
				Ref<Texture2D> icon = p_editor->get_icon();
				if (icon.is_valid()) {
					tb->set_icon(icon);
				} else if (singleton->gui_base->has_theme_icon(p_editor->get_name(), SNAME("EditorIcons"))) {
					tb->set_icon(singleton->gui_base->get_theme_icon(p_editor->get_name(), SNAME("EditorIcons")));
				}
			}
			_build_icon_type_cache();
			prev_scene->set_icon(gui_base->get_theme_icon(SNAME("PrevScene"), SNAME("EditorIcons")));
			distraction_free->set_icon(gui_base->get_theme_icon(SNAME("DistractionFree"), SNAME("EditorIcons")));
			scene_tab_add->set_icon(gui_base->get_theme_icon(SNAME("Add"), SNAME("EditorIcons")));
			bottom_panel_raise->set_icon(gui_base->get_theme_icon(SNAME("ExpandBottomDock"), SNAME("EditorIcons")));
			if (gui_base->is_layout_rtl()) {
				dock_tab_move_left->set_icon(theme->get_icon(SNAME("Forward"), SNAME("EditorIcons")));
				dock_tab_move_right->set_icon(theme->get_icon(SNAME("Back"), SNAME("EditorIcons")));
			} else {
				dock_tab_move_left->set_icon(theme->get_icon(SNAME("Back"), SNAME("EditorIcons")));
				dock_tab_move_right->set_icon(theme->get_icon(SNAME("Forward"), SNAME("EditorIcons")));
			}
			help_menu->set_item_icon(help_menu->get_item_index(HELP_SEARCH), gui_base->get_theme_icon(SNAME("HelpSearch"), SNAME("EditorIcons")));
			help_menu->set_item_icon(help_menu->get_item_index(HELP_DOCS), gui_base->get_theme_icon(SNAME("ExternalLink"), SNAME("EditorIcons")));