mpool.ByteSlicePool leak

[xux1217]

		b, err := mp.readNext()
		if err != nil {
			mp.shutdownErr = err
			return
		}
		
		mp.chLock.Lock()
		msch, ok := mp.channels[ch]
		mp.chLock.Unlock()

		switch tag {
		case newStreamTag:
			if ok {
				log.Debugf("received NewStream message for existing stream: %d", ch)
				mp.shutdownErr = ErrInvalidState
				return
			}

			name := string(b)
			msch = mp.newStream(ch, name)
			mp.chLock.Lock()
			mp.channels[ch] = msch
			mp.chLock.Unlock()
			select {
			case mp.nstreams <- msch:
			case <-mp.shutdown:
				return
			}

b, err := mp.readNext() get a byte buffer, but in case newStreamTag: branch, the b doesn't put to mpool.ByteSlicePool.

[xux1217]

in multiplex.go:259