Don't call freeaddrinfo() when getaddrinfo() fails

POSIX is somewhat unclear here, but doing so segfaults on some platforms.  Hat tip Kamil Slowikowski @slowkow.  Instead print a more detailed error message using gai_strerror().

This is a **klib** fix for lh3/samtools#21; see also http://sourceforge.net/p/samtools/mailman/message/32229136/