(isc_check_read_callback): Don't crash if wr_msg_q is NULL.

(isc_check_read_callback): Don't setup any callbacks in
	ISC_STATE_CLOSING.

src/libraries/libisc-new/src/isc_session.c

@@ -297,8 +297,9 @@ isc_check_read_callback(struct isc_scb_internal *session,
 
   /* Too many queued blocks or bytes?  Don't read any more data, until
      the client has read the output we have already produced. */
-  if (isc_sizequeue(session->wr_msg_q) >= session->cfg->max.queuedsize
-      || session->wr_msg_q->bytes >= session->cfg->max.queuedsize_bytes)
+  if (session->wr_msg_q != NULL
+      && (isc_sizequeue(session->wr_msg_q) >= session->cfg->max.queuedsize
+	  || session->wr_msg_q->bytes >= session->cfg->max.queuedsize_bytes))
   {
     want_read = 0;
     want_write_timeout = 1;
@@ -307,6 +308,13 @@ isc_check_read_callback(struct isc_scb_internal *session,
   if (session->state == ISC_STATE_DISABLED)
     want_read = 0;
 
+  /* If this session is closing down there is no need for callbacks.  */
+  if (session->state == ISC_STATE_CLOSING)
+  {
+    want_read = 0;
+    want_write_timeout = 0;
+  }
+
   if (!want_read)
     isc_cancel_read_callback(session);
   else if (!session->data_available_registered
@@ -334,7 +342,7 @@ isc_check_read_callback(struct isc_scb_internal *session,
     session->stale_output_cb_registered = 1;
   }
 
-  if (!session->idle_cb_registered)
+  if (!session->idle_cb_registered && session->state != ISC_STATE_CLOSING)
   {
     setup_timer(&session->idle_tv, session->acceptable_idle_time);
     source->on_time(source, session->idle_tv, idle_cb, session);