Fixed loading of stat cache entries into the wrong key

* Silly bug from 2afdc066f52b54faf63f9c980f7ef6a7841dd094 which caused HEAD
  requests. Probably missed in local testing due to memcached.

Change-Id: I3b82ffe964e252eafa5254f7752e5ba45b49ba0e
(cherry picked from commit 519883bd67c960998e8cb2eb0cda52f3764192f7)