[chore:] adapt button enabeling to existance of PersonErrors

MainWindow.axaml.cs

@@ -698,10 +698,23 @@ public partial class MainWindow : Window
             BtnCheck.IsEnabled = true;
             BtnCombine.IsEnabled = true;
             BtnGenerateLabels.IsEnabled = true;
-            BtnShorten.IsEnabled = true;
+            
+            // check for existing errors, otherwise disable the features
+            foreach(KasPerson pers in (LstCustomerAdressSets.SelectedItem as KasAddressList).KasPersons)
+                if (pers.PersonError != null)
+                {
+                    BtnShorten.IsEnabled = true;
+                    // BtnRepair.IsEnabled = true;
+                    break;
+                }
+                else
+                {
+                    BtnShorten.IsEnabled = false;
+                    BtnRepair.IsEnabled = false;
+                }
 
-            // BtnRepair.IsEnabled = true;
+            
-            // BtnShorten.IsEnabled = true;
+            
         }
     }