When compiled with musl >1.1.20, fastd will crash in case it can't
resolve a peers hostname. This is due to a changed implementation of
freeaddrinfo in musl 1.1.21 onwards.

This segfault is fixed by not calling freeaddrinfo in case the supplied
pointer is null.

Signed-off-by: David Bauer <mail@david-bauer.net>