exit when exception encountered (dotnet#216)

Author: srsaggam

src/mlnet/Commands/New/NewCommandHandler.cs

@@ -41,6 +41,7 @@ public void Execute()
                 logger.Log(LogLevel.Error, e.Message);
                 logger.Log(LogLevel.Debug, e.ToString());
                 logger.Log(LogLevel.Error, Strings.Exiting);
+                return;
             }
 
             // Sanitize columns