Avoid "Undefined index" error in project.search API when project_customfieldstorage table has additional fields not requested

Summary:
Do not trigger an "Undefined index" error in PhabricatorCustomFieldStorage when calling the `project.search` Conduit API without passing search parameters when the local project_customfieldstorage table has additional fields configured not requested in the API call.

Closes T15688

Test Plan: See above; `curl -k -s -X GET http://phorge.localhost/api/project.search?api.token=api-xxxxxxxxxxxx | jq -r` for comparison

Reviewers: O1 Blessed Committers, 20after4

Reviewed By: O1 Blessed Committers, 20after4

Subscribers: 20after4, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15688

Differential Revision: https://we.phorge.it/D25493

src/infrastructure/customfield/storage/PhabricatorCustomFieldStorage.php

@@ -80,6 +80,10 @@ abstract class PhabricatorCustomFieldStorage
       $object_phid = $row['objectPHID'];
       $value = $row['fieldValue'];
 
+      if (!isset($map[$index]) || !isset($map[$index][$object_phid])) {
+       continue;
+      }
+
       $key = $map[$index][$object_phid];
       $result[$key] = $value;
     }