CCBC-180 Do not destroy event struct in release_socket()

Segmentation fault when the hostname resolved into several addresses
and first of them reject couchbase connections. In this case
libcouchbase releases socket and destroys the the event structure, so
that subsequent calls will try to dereference NULL-event.

Change-Id: I963691e36e21d9e8c322f9dc9e5c9ec36e02ba37
Reviewed-on: http://review.couchbase.org/24620
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>