Merge branch '1623-assertion-failure-ns-client-endrequest' into 'master'

Don't issue ns_client_endrequest on a NS_CLIENTSTATE_READY client.

Closes #1623

See merge request isc-projects/bind9!3077

lib/ns/client.c

@@ -1577,6 +1577,14 @@ ns__client_reset_cb(void *client0) {
 	ns_client_log(client, DNS_LOGCATEGORY_SECURITY, NS_LOGMODULE_CLIENT,
 		      ISC_LOG_DEBUG(3), "reset client");
 
+	/*
+	 * We never started processing this client, possible if we're
+	 * shutting down, just exit.
+	 */
+	if (client->state == NS_CLIENTSTATE_READY) {
+		return;
+	}
+
 	ns_client_endrequest(client);
 	if (client->tcpbuf != NULL) {
 		isc_mem_put(client->mctx, client->tcpbuf,