Improve exception when creating a cyclic dependency in Maniphest

Summary: Fixes T6815. This was overlooked in D9838. This could be prettier, but does the job.

Test Plan: {F327790}

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T6815

Differential Revision: https://secure.phabricator.com/D11937

src/applications/search/controller/PhabricatorSearchAttachController.php

@@ -84,9 +84,14 @@ final class PhabricatorSearchAttachController
             '+' => array_fuse($add_phids),
             '-' => array_fuse($rem_phids),
           ));
-        $txn_editor->applyTransactions(
-          $object->getApplicationTransactionObject(),
-          array($txn_template));
+
+        try {
+          $txn_editor->applyTransactions(
+            $object->getApplicationTransactionObject(),
+            array($txn_template));
+        } catch (PhabricatorEdgeCycleException $ex) {
+          $this->raiseGraphCycleException($ex);
+        }
 
         return id(new AphrontReloadResponse())->setURI($handle->getURI());
       } else {