AESinkALSA: Workaround alsa-lib buffer overflow in snd_pcm_chmap_print

snd_pcm_chmap_print() seems to contain a bug that can cause it to overrun the buffer provided to it in certainc cases. Provide a double-length buffer for it, which the buggy versions cannot overflow.

There might be some other bug in there as well since the channel map string is suspiciously long (64+ chars) if this buffer overflow was indeed actually triggered, but that would be a separate issue.

http://trac.kodi.tv/ticket/15641
http://mailman.alsa-project.org/pipermail/alsa-devel/2014-December/085815.html