Refine "invalid cursor" exception to have a little more information

Summary: Ref T8780.

Test Plan: See @chad.

Reviewers: chad

Reviewed By: chad

Subscribers: chad, epriestley

Maniphest Tasks: T8780

Differential Revision: https://secure.phabricator.com/D13583

src/infrastructure/query/policy/PhabricatorCursorPagedPolicyAwareQuery.php

@@ -410,8 +410,9 @@ abstract class PhabricatorCursorPagedPolicyAwareQuery
     if (!$object) {
       throw new Exception(
         pht(
-          'Cursor "%s" does not identify a valid object.',
+          'Cursor "%s" does not identify a valid object in query "%s".',
-          $cursor));
+          $cursor,
+          get_class($this)));
     }
 
     return $object;