CON-2300 | WikiaPageType Fatal error fix

[LinkCache::getGoodLinkFieldObj()](https://github.com/Wikia/app/blob/dev/includes/cache/LinkCache.php#L66) calls [LinkCache::getMemcKey()](https://github.com/Wikia/app/blob/dev/includes/cache/LinkCache.php#L267) which may return a non-null value even when there is no redirect target. The implementation looks poor at the first glance. Try to set `$wgEnableFastLinkCache` for one wiki to `false` and redo your test and see if it still returns `true`. Looks like it is a false positive.