fix(ldap): pagination for PHP 7.4 & 8.0

After PR symfony#38392 there is a little issue in the Symfony code base that
occurs only for PHP 7.4 and PHP 8.0.

This is related to issue symfony#38874

src/Symfony/Component/Ldap/Adapter/ExtLdap/Query.php

@@ -174,8 +174,7 @@ public function getResources(): array
     private function resetPagination()
     {
         $con = $this->connection->getResource();
-        $this->controlPagedResultResponse($con, 0, '');
-        $this->serverctrls = [];
+        $this->controlPagedResultResponse($con, null, '');
 
         // This is a workaround for a bit of a bug in the above invocation
         // of ldap_control_paged_result. Instead of indicating to extldap that
@@ -226,16 +225,23 @@ private function controlPagedResult($con, int $pageSize, string $cookie): bool
     /**
      * Retrieve LDAP pagination cookie.
      *
-     * @param resource $con
-     * @param resource $result
+     * @param resource      $con
+     * @param resource|null $result
      */
     private function controlPagedResultResponse($con, $result, string $cookie = ''): string
     {
+        $this->serverctrls = [];
+
         if (\PHP_VERSION_ID < 70300) {
             ldap_control_paged_result_response($con, $result, $cookie);
 
             return $cookie;
         }
+
+        if (null === $result) {
+            return '';
+        }
+
         ldap_parse_result($con, $result, $errcode, $matcheddn, $errmsg, $referrals, $controls);
 
         return $controls[\LDAP_CONTROL_PAGEDRESULTS]['value']['cookie'] ?? '';