### 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
for (int i = 0; i < DOCK_SLOT_MAX; i++) {
		String names;
		for (int j = 0; j < dock_slot[i]->get_tab_count(); j++) {
			String name = dock_slot[i]->get_tab_control(j)->get_name();
			if (!names.is_empty()) {
				names += ",";
			}
			names += name;
		}
		String config_key = "dock_" + itos(i + 1);
		if (p_layout->has_section_key(p_section, config_key)) {
			p_layout->erase_section_key(p_section, config_key);
		}
		if (!names.is_empty()) {
			p_layout->set_value(p_section, config_key, names);
		}
		int selected_tab_idx = dock_slot[i]->get_current_tab();