libsndfile: add fix for alaw and ulaw issues

This fix addresses CVE-2018-19661, CVE-2018-19662, CVE-2017-17456 and
CVE-2017-17457.

CVE-2017-14245 and CVE-2017-14246 are fixed as well since they are
duplicates of CVE-2017-17456 and CVE-2017-17457.

I have already asked for rejection when appropriate but didn't get any
answer from the mitre team yet.