BUG 10156 Cron execution stop if an error is found in any event SOLVED

- To run cron was stopped in one case in the function PMFGetUserEmailAddress for a nonexistent user id.
- was add validation to nonexistent user

workflow/engine/classes/class.pmFunctions.php

@@ -2394,9 +2394,11 @@ function PMFGetUserEmailAddress ($id, $APP_UID = null, $prefix = 'usr')
                     }
                 } else {
                     $oUserRow = UsersPeer::retrieveByPK( $sID );
-                    $sID = $oUserRow->getUsrEmail();
-                    if (G::emailAddress( $sID )) {
-                        array_push( $aRecipient, $sID );
+                    if ($oUserRow != null) {
+                        $sID = $oUserRow->getUsrEmail();
+                        if (G::emailAddress( $sID )) {
+                            array_push( $aRecipient, $sID );
+                        }
                     }
                 }