ss6 branch - Issues if no key set (eg local)

[josephlewisnz]

If no keys set then the module still attempts to purge pages, ultimately erroring out.

eg.

[Deprecated] str_replace(): Passing null to parameter #2 ($replace) of type array|string is deprecated
POST /admin/pages/edit/EditForm/431
Line 406 in /var/www/html/vendor/catalyst.net.nz/silverstripe-cloudflare/src/Purge/Purge.php

Source
397         return $output;
398     }
399 
400     /**
401      * @return string
402      */
403     public function getEndpoint()
404     {
405         $zoneId = CloudFlare::singleton()->fetchZoneID();
406         return str_replace(":identifier", $zoneId, static::$endpoint);
407     }

Ideally, we just shouldn't be calling purge if no keys set