Only increase the counter when we do take a wakelock

We keep track on how many wakelocks we have taken. We always
just take one real wakelock but increase / decrease the
counter every time we try to acquire / release a wakelock.
The counter is always increased even if the power manager is
not ready, leading to an incorrect counter that could cause a
crash when we try to release it.
Make sure we only increase the counter when a wakelock, real
or counted, is taken.

Change-Id: Iad940e052694932f1dad8a1a71fa63601d289d6a