[libvirt] CVE-2014-1447 [was: [PATCH] Really don't crash if a connection closes early]

https://bugzilla.redhat.com/show_bug.cgi?id=1047577 When writing commit 173c291, I missed the fact virNetServerClientClose unlocks the client object before actually clearing client->sock and thus it is possible to hit a window when client->keepalive is NULL while client->sock is not NULL. I was thinking client->sock == NULL was a better check for a closed connection but apparently we have to go with client->keepalive == NULL to actually fix the crash.