tinysvcmdns: fix CVE-2017-12087

tinysvcmdns: fix CVE-2017-12087

This patch incorporates upstream's fixes for a remotely exploitable
buffer overflow bug in the bundled tinysvcmdns library. The following
upstream commits are included:

https://bitbucket.org/geekman/tinysvcmdns/commits/48c73fbb36b7a5584b00538d89c89dd8b15ab2a7
https://bitbucket.org/geekman/tinysvcmdns/commits/29ea1b9fca94dc42d16109e050d2967231b1e341

The changes have been incorporated preserving local changes such as the
check for malloc() returning NULL.

Reported against shairport-sync in Ubuntu Launchpad:
https://bugs.launchpad.net/ubuntu/+source/shairport-sync/+bug/1729668

This commit closes GitHub issue #619.