Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=51813

Add NULL-checking for s->net to avoid SIGSEGV in situations where it appears a socket has been recycled.


git-svn-id: https://svn.apache.org/repos/asf/tomcat/native/branches/1.1.x@1518225 13f79535-47bb-0310-9956-ffa450edef68