ALSA: fix deadlock under some circumstances
ALSA: fix deadlock under some circumstances

If the write_callback came upon an error during the prepare
phase, and never wrote any frames to the hardware buffer,
and another thread tried to soundio_outstream_destroy, this
would cause a deadlock.

This is now fixed.

tresf/libsoundio,tresf/libsoundio,andrewrk/libsoundio,andrewrk/libsoundio