if no CFs were listed as mandatory then all were mandatory

For example the following config were causing all CFs to
be mandatory:

    'Tech Support' => {
         '* -> resolved' => [ 'TimeWorked', 'TimeTaken', 'Content' ],
    },

Thanks to David Prangnell and Josh Jenkins.

lib/RT/Extension/MandatoryOnTransition.pm

@@ -356,6 +356,8 @@ sub CheckMandatoryFields {
                                      $label, $ARGSRef->{Status});
     }
 
+    return \@errors unless @$cfs;
+
     if ( not $CFs ){
         $RT::Logger->error("Custom Fields object required to process mandatory custom fields");
         return \@errors;