Fixing possible race condition.

That return statement is effectively a reading of asynchronously modified
field. The reading and writing is elsewhere protected by locking on thread
instance, except this one occurence. Moving 'return' statement into
synchronized block ensures that it reads updated value.

Don't be afraid of deadlock - wait() releases the lock and acquires it
back when notified.

Change-Id: I940c24c04a1a2d4508d14d11b6174ff4fb2ab7d5