libvorbis: add upstream security fixes

libvorbis: add upstream security fixes

Fixes the following security issues:

CVE-2017-14632: Libvorbis 1.3.5 allows Remote Code Execution upon freeing
uninitialized memory in the function vorbis_analysis_headerout() in info.c
when vi->channels<=0, a similar issue to Mozilla bug 550184.

CVE-2017-14633: In libvorbis 1.3.5, an out-of-bounds array read
vulnerability exists in the function mapping0_forward() in mapping0.c, which
may lead to DoS when operating on a crafted audio file with
vorbis_analysis().

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>