CRM-12042 edge case protection

CRM/Core/Payment/BaseIPN.php

@@ -725,6 +725,11 @@ LIMIT 1;";
 
       // we have a pledge now we need to get the oldest unpaid payment
       $paymentDetails = CRM_Pledge_BAO_PledgePayment::getOldestPledgePayment($pledgeId);
+      if(empty($paymentDetails['id'])){
+        // we can assume this pledge is now completed
+        // return now so we don't create a core error & roll back
+        return;
+      }
       $paymentDetails['contribution_id'] = $contribution->id;
       $paymentDetails['status_id'] = $contribution->contribution_status_id;
       $paymentDetails['actual_amount'] = $contribution->total_amount;