### 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
if (singleton->cmdline_export_mode) {
		print_line("\t" + p_task + ": step " + itos(p_step) + ": " + p_state);
		return false;
	} else if (singleton->progress_dialog) {
		return singleton->progress_dialog->task_step(p_task, p_state, p_step, p_force_refresh);
	} else {
		return false;
	}
}
void EditorNode::progress_end_task(const String &p_task) {
	if (singleton->cmdline_export_mode) {
		print_line(p_task + ": end");
	} else if (singleton->progress_dialog) {
		singleton->progress_dialog->end_task(p_task);
	}
}
void EditorNode::progress_add_task_bg(const String &p_task, const String &p_label, int p_steps) {
	singleton->progress_hb->add_task(p_task, p_label, p_steps);
}
void EditorNode::progress_task_step_bg(const String &p_task, int p_step) {
	singleton->progress_hb->task_step(p_task, p_step);
}
void EditorNode::progress_end_task_bg(const String &p_task) {
	singleton->progress_hb->end_task(p_task);
}
String EditorNode::_get_system_info() const {