Use ones compiliment so we don't kill previously set flags..

This commit was SVN r9428.

ompi/datatype/convertor.c

@@ -229,7 +229,7 @@ int32_t ompi_convertor_set_position_nocheck( ompi_convertor_t* convertor,
     }
 
     /* Remove the completed flag if it's already set */
-    convertor->flags &= !CONVERTOR_COMPLETED;
+    convertor->flags &= ~CONVERTOR_COMPLETED;
 
     /*
      * If we plan to rollback the convertor then first we have to set it