Fixed bug that caused 100% CPU usage if soundcard is unplugged

Pass G_IO_ERR to asound_poll_cb, and exit gracefully if an error happens. Without this, it never passes the error and infinitely loops as fast as it can, causing 100% CPU utilization.

Signed-off-by: Steven Honeyman <stevenhoneyman@users.noreply.github.com>
Merge pull request #37 from stevenhoneyman/fixes-for-upstream

Fix bug causing 100 % CPU usage if soundcard is unplugged