Replaced port area helper and avoided crash when searching at a harbour that has no entries

ENI2/DetailViewControls/PortNotificationDetailControl.xaml.cs

@@ -523,10 +523,12 @@ namespace ENI2.DetailViewControls
 
         private void buttonSearchPortArea_Click(object sender, RoutedEventArgs e)
         {
-            SelectPortAreaDialog spad = new SelectPortAreaDialog(this.Core.PoC);
-            if(spad.ShowDialog() ?? false)
+            if (portAreas != null)
             {
-                if(spad.SelectedArea != null)
+                SelectPortAreaDialog spad = new SelectPortAreaDialog(this.Core.PoC);
+                if (spad.ShowDialog() ?? false)
+                {
+                    if (spad.SelectedArea != null)
                     {
                         if (portAreas.ContainsKey(spad.SelectedArea))
                         {
@@ -536,6 +538,7 @@ namespace ENI2.DetailViewControls
                     }
                 }
             }
+        }
 
         #endregion