Respect WEBSOCKET_OPCODE_CONNECTION_CLOSE coming from client

mongoose.c

@@ -3032,7 +3032,8 @@ static size_t deliver_websocket_frame(struct connection *conn) {
     }
 
     // Call the handler and remove frame from the iobuf
-    if (call_user(conn, MG_REQUEST) == MG_FALSE) {
+    if (call_user(conn, MG_REQUEST) == MG_FALSE ||
+        (buf[0] & 0x0f) == WEBSOCKET_OPCODE_CONNECTION_CLOSE) {
       conn->ns_conn->flags |= NSF_FINISHED_SENDING_DATA;
     }
     iobuf_remove(&conn->ns_conn->recv_iobuf, frame_len);