Fixed frame length issue exceeding short value

Thanks to Michael Niendorf for the report and fix

Author: mondain

src/main/java/org/red5/net/websocket/codec/WebSocketDecoder.java

@@ -441,7 +441,7 @@ public static void decodeIncommingData(IoBuffer in, IoSession session) {
             decoderState.frameLen = (frameInfo2 & (byte) 0x7F);
             log.trace("Payload length: {}", decoderState.frameLen);
             if (decoderState.frameLen == 126) {
-                decoderState.frameLen = in.getShort();
+                decoderState.frameLen = in.getUnsignedShort();
                 log.trace("Payload length updated: {}", decoderState.frameLen);
             } else if (decoderState.frameLen == 127) {
                 long extendedLen = in.getLong();
@@ -582,4 +582,4 @@ public static Map<String, Object> parseQuerystring(String query) {
         return map;
     }
 
-}
+}