upgrade hook to fix existing hook urls

CRM/Zapier/Upgrader.php

@@ -26,8 +26,11 @@ class CRM_Zapier_Upgrader extends CRM_Extension_Upgrader_Base {
     $val = Civi::settings()->get('zapierHooks');
     if (self::is_serialized($val)) {
       $val = unserialize($val);
-      if (is_array($val)) {
-        Civi::settings()->set('zapierHooks', $val);
+      if (self::is_serialized($val)) {
+        $val = unserialize($val);
+        if (is_array($val)) {
+          Civi::settings()->set('zapierHooks', $val);
+        }
       }
     }