Fix watcher query to work correctly with no watchers.

src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php

@@ -1922,7 +1922,7 @@ abstract class PhabricatorApplicationTransactionEditor
         $query->execute();
 
         $watcher_phids = $query->getDestinationPHIDs();
-
+        if ($watcher_phids) {
           // We need to do a visibility check for all the watchers, as
           // watching a project is not a guarantee that you can see objects
           // associated with it.
@@ -1941,6 +1941,7 @@ abstract class PhabricatorApplicationTransactionEditor
             }
           }
         }
+      }
 
       $has_support = true;
     }