update try catch on Ampt class

csharp/Lib/Devices/AMPT/AmptDevices.cs

@@ -33,7 +33,9 @@ public class AmptDevices
         }
         catch ( Exception e)
         {
+            if( e is not NullChannelException)
                 Console.WriteLine("Failed to read Ampt data \n" + e.Message);
+
             return null;
         }
     }