add missing safety check to selection decoration parser

Had been meaning to have put it in from the beginning, but forgot.


Former-commit-id: 2c67a02fd11a2627af296095071392e324a0bedf

PhysicsAnalysis/Algorithms/SelectionHelpers/Root/ISelectionAccessor.cxx

@@ -64,6 +64,12 @@ namespace CP
       }
     }
 
+    if (asChar && asBits)
+    {
+      ANA_MSG_ERROR ("can't specify both 'as_bits' and 'as_char' for the same selection decoration, pick one!!!");
+      return StatusCode::FAILURE;
+    }
+
     if (!asChar && !asBits)
     {
       if (defaultToChar)