Fixed problem with login check within Chrome 33.x and auto-completion

Same patch previously applied in other files. ajax.php was missed at
that time.

https://github.com/cosmocode/contagged/commit/e6398bad6d0293d1c7da37a410ae7e359895c41e

Incidentally it restore the auto-completion feature within Contagged
editor page.
Merge pull request #13 from marcovanbeek/master

Fixed problem with login check within Chrome 33.x and auto-completion