### 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
int center_split_offset = center_split->get_split_offset();
	p_config_file->set_value(EDITOR_NODE_CONFIG_SECTION, "center_split_offset", center_split_offset);
	int selected_bottom_panel_item_idx = -1;
	for (int i = 0; i < bottom_panel_items.size(); i++) {
		if (bottom_panel_items[i].button->is_pressed()) {
			selected_bottom_panel_item_idx = i;
			break;
		}
	}
	if (selected_bottom_panel_item_idx != -1) {
		p_config_file->set_value(EDITOR_NODE_CONFIG_SECTION, "selected_bottom_panel_item", selected_bottom_panel_item_idx);
	} else {
		p_config_file->set_value(EDITOR_NODE_CONFIG_SECTION, "selected_bottom_panel_item", Variant());
	}
	
	int selected_default_debugger_tab_idx = EditorDebuggerNode::get_singleton()->get_default_debugger()->get_current_debugger_tab();
	p_config_file->set_value(EDITOR_NODE_CONFIG_SECTION, "selected_default_debugger_tab_idx", selected_default_debugger_tab_idx);
	
	int selected_main_editor_idx = -1;
	for (int i = 0; i < main_editor_buttons.size(); i++) {
		if (main_editor_buttons[i]->is_pressed()) {
			selected_main_editor_idx = i;
			break;
		}
	}
	if (selected_main_editor_idx != -1) {
		p_config_file->set_value(EDITOR_NODE_CONFIG_SECTION, "selected_main_editor_idx", selected_main_editor_idx);
	} else {