*) core: Be safe with ap_lingering_close() called with a socket NULL-ed.

*) core: Be safe with ap_lingering_close() called with a socket NULL-ed.

PR 65627.

mod_itk seems to:
  ap_set_core_module_config(c->conn_config, NULL)
before calling ap_lingering_close(), causing a crash after r1891721.
Until we have an API to no-op ap_lingering_close(), let's be safe.

* server/connection.c(ap_start_lingering_close):
  The socket should not be NULL here, add an assertion.

* server/connection.c(ap_lingering_close):
  Set c->aborted if the socket is NULL, and give up.

Submitted by: acmondor <bz.apache.org acmondor.ca>, ylavic

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1894171 13f79535-47bb-0310-9956-ffa450edef68