Fix PaypalIPN single function to not receive-by-reference

The function is called from 2 places
- main
- recur

In both cases it is at the end of the function & so the vars, if altered, are not used again.
In the case of main they are internal to the function whereas for recur they are not returned to the
calling function

CRM/Core/Payment/PayPalIPN.php

@@ -229,8 +229,10 @@ public function recur($input, $ids, $objects, $first) {
    * @param bool $first
    *
    * @return void
+   * @throws \CRM_Core_Exception
+   * @throws \CiviCRM_API3_Exception
    */
-  public function single(&$input, &$ids, &$objects, $recur = FALSE, $first = FALSE) {
+  public function single($input, $ids, $objects, $recur = FALSE, $first = FALSE) {
     $contribution = &$objects['contribution'];
 
     // make sure the invoice is valid and matches what we have in the contribution record
@@ -257,15 +259,15 @@ public function single(&$input, &$ids, &$objects, $recur = FALSE, $first = FALSE
     }
 
     $status = $input['paymentStatus'];
-    if ($status == 'Denied' || $status == 'Failed' || $status == 'Voided') {
+    if ($status === 'Denied' || $status === 'Failed' || $status === 'Voided') {
       $this->failed($objects);
       return;
     }
     if ($status === 'Pending') {
       Civi::log()->debug('Returning since contribution status is Pending');
       return;
     }
-    elseif ($status == 'Refunded' || $status == 'Reversed') {
+    elseif ($status === 'Refunded' || $status === 'Reversed') {
       $this->cancelled($objects);
       return;
     }
@@ -369,7 +371,7 @@ public function main() {
         return;
       }
     }
-    $this->single($input, $ids, $objects, FALSE, FALSE);
+    $this->single($input, $ids, $objects);
   }
 
   /**