Add default option to switch statement

Fixes enumeration value not handled in switch [-Wswitch] error

modules/advancedusvis/pipelines/advancedusvis.cpp

@@ -223,6 +223,8 @@ namespace campvis {
                 case tgt::KeyEvent::K_DOWN:
                     _usFusion1.p_sliceNumber.decrement();
                     break;
+                default:
+                    break;
             }
         }
     }
@@ -237,4 +239,4 @@ namespace campvis {
         }
     }
 
-}
\ No newline at end of file
+}