websocket decoder: skip payload unmasking if mask is 0

Author: mostroverkhov

netty-websocket-http1/src/main/java/com/jauntsdn/netty/handler/codec/http/websocketx/WebSocketMaskedDecoder.java

@@ -487,6 +487,10 @@ void closeInbound() {
   }
 
   static void unmask(ByteBuf payload, int mask) {
+    if (mask == 0) {
+      return;
+    }
+
     int readableBytes = payload.readableBytes();
     int cur = 0;