wasapi: fix two crashes (Bug 1340278, Bug 1340289)
wasapi: fix two crashes (Bug 1340278, Bug 1340289)

* Forget the emergency_bailout bool on the non-rendering thread when using it to do an emergency bailout.

* Lock before asserting: even when in an assert, touching output_client or input_client has to be done while locked.

* Paranoia: if the pointer to the emergency bailout boolean is null on rendering thread start, return immediately.

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