LibGUI: Add break even before empty default label

Clang is a bit more pedantic than GCC when diagnosing implicit
fallthroughs, and doesn't care if the succeeding label only contains a
single break statement.

Userland/Libraries/LibGUI/VimEditingEngine.cpp

@@ -995,6 +995,7 @@ bool VimEditingEngine::on_key_in_normal_mode(const KeyEvent& event)
             }
             case (KeyCode::Key_P):
                 put_before();
+                break;
             default:
                 break;
             }