lcb_gai2sock_v1() might return NULL, check for it before using

Change-Id: Ib17c8c9a544f1d506f5bf3e45fc743b7553acc97
Reviewed-on: http://review.couchbase.org/28934
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>