Backport of upstream r1894171 to fix segfaults with mpm-itk.

https://bugs.gentoo.org/816258
https://bz.apache.org/bugzilla/show_bug.cgi?id=65627

--- a/server/connection.c	2021/09/21 20:03:52	1893497
+++ b/server/connection.c	2021/10/12 16:48:18	1894171
@@ -145,9 +145,7 @@
 {
     apr_socket_t *csd = ap_get_conn_socket(c);
 
-    if (!csd) {
-        return 1;
-    }
+    ap_assert(csd != NULL);
 
     if (ap_prep_lingering_close(c)) {
         return 1;
@@ -178,6 +176,15 @@
     apr_time_t now, timeup = 0;
     apr_socket_t *csd = ap_get_conn_socket(c);
 
+    if (!csd) {
+        /* Be safe with third-party modules that:
+         *   ap_set_core_module_config(c->conn_config, NULL)
+         * to no-op ap_lingering_close().
+         */
+        c->aborted = 1;
+        return;
+    }
+
     if (ap_start_lingering_close(c)) {
         apr_socket_close(csd);
         return;