Don't put bad mailing list names in the CC list of a commit message

Summary:
If we can't look up the name for a mailing list, don't put 'Unknown Mailing
List' in the commit message - it will confuse things later down the road.

Surely there is a better way of doing this than checking the name of the
handle for the mailing list.

Test Plan:
called differential.getcommitmessage on a revision that had an invalid mailing
list phid.

Reviewers: epriestley, schrockn, jungejason

Reviewed By: epriestley

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D1910

src/applications/differential/field/specification/ccs/DifferentialCCsFieldSpecification.php

@@ -114,7 +114,10 @@ final class DifferentialCCsFieldSpecification
 
     $names = array();
     foreach ($this->ccs as $phid) {
-      $names[] = $this->getHandle($phid)->getName();
+      $handle = $this->getHandle($phid);
+      if ($handle->isComplete()) {
+        $names[] = $handle->getName();
+      }
     }
     return implode(', ', $names);
   }