### 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
ofs.y += s.y;
			} break;
			case DOCK_SLOT_LEFT_UR: {
				ofs.x += s.x;
			} break;
			case DOCK_SLOT_LEFT_BR: {
				ofs += s;
			} break;
			case DOCK_SLOT_RIGHT_UL: {
				ofs.x += s.x * 4;
			} break;
			case DOCK_SLOT_RIGHT_BL: {
				ofs.x += s.x * 4;
				ofs.y += s.y;
			} break;
			case DOCK_SLOT_RIGHT_UR: {
				ofs.x += s.x * 4;
				ofs.x += s.x;
			} break;
			case DOCK_SLOT_RIGHT_BR: {
				ofs.x += s.x * 4;
				ofs += s;
			} break;
		}
		Rect2 r(ofs, s);
		dock_select_rect[i] = r;
		r.position += Vector2(2, 5);
		r.size -= Vector2(4, 7);
		if (i == dock_select_rect_over_idx) {
			dock_select->draw_rect(r, used_selected);