### 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
dock_popup_selected_idx = p_which;
}
void EditorNode::_dock_move_left() {
	if (dock_popup_selected_idx < 0 || dock_popup_selected_idx >= DOCK_SLOT_MAX) {
		return;
	}
	Control *current_ctl = dock_slot[dock_popup_selected_idx]->get_tab_control(dock_slot[dock_popup_selected_idx]->get_current_tab());
	Control *prev_ctl = dock_slot[dock_popup_selected_idx]->get_tab_control(dock_slot[dock_popup_selected_idx]->get_current_tab() - 1);
	if (!current_ctl || !prev_ctl) {
		return;
	}
	dock_slot[dock_popup_selected_idx]->move_child(current_ctl, prev_ctl->get_index(false));
	dock_select->queue_redraw();
	_edit_current();
	_save_editor_layout();
}
void EditorNode::_dock_move_right() {
	Control *current_ctl = dock_slot[dock_popup_selected_idx]->get_tab_control(dock_slot[dock_popup_selected_idx]->get_current_tab());
	Control *next_ctl = dock_slot[dock_popup_selected_idx]->get_tab_control(dock_slot[dock_popup_selected_idx]->get_current_tab() + 1);
	if (!current_ctl || !next_ctl) {
		return;
	}
	dock_slot[dock_popup_selected_idx]->move_child(next_ctl, current_ctl->get_index(false));
	dock_select->queue_redraw();
	_edit_current();
	_save_editor_layout();
}
void EditorNode::_dock_select_draw() {