LockBackendInterface::wait() needs to be followed by another attempt to acquire the lock

[bradbulger]

This relates to the locking code from Chapter 14 on.

From the comments in the code: "You still need to acquire the lock manually and it may fail again."

An example use is in PrivateTempStore::set(). You have to follow a return of FALSE from wait() with a second acquire() to actually claim the lock.

[nithikpackt]

Thank you @bradbulger for the solution