Fixing the  Undefined index: pager error

Not sure why $GLOBALS['pager']; is empty at some times (the site was working fine, at some random refresh it failed, deleted the caching but still no avail).

Since it wasn't doing a proper exist check in any case I've added it until we get rid of the $GLOBALS part :)
Merge pull request #570 from CoolGoose/patch-2

Fixing the  Undefined index: pager error