Bug fix for GUI, visQuantity warning popup

Author: remocristoforetti

matRad/gui/widgets/matRad_ViewingWidget.m

@@ -1146,6 +1146,8 @@ function initValues(this)
                             otherwise
                                 visQuantity = [];
                         end
+                    else
+                        visQuantity = [];
                     end
 
                     if isfield(pln,'propStf')