fix hang on thread creation failure

with assertions enabled the code would abort in
WebPWorkerChangeState with:
Assertion `worker->status_ >= OK'

without them the code would hang in the _cond_wait.

this change makes WebPWorkerChangeState a no-op in this case.

Change-Id: Iea855568bbdef2865ae61ab54473b3a7c230e91a
1 file changed