Don't need to consider the case ReadableByteChannel#read returns 0

since the buffer size must be more than 0

Author: komamitsu

msgpack-core/src/main/java/org/msgpack/core/buffer/ChannelBufferInput.java

@@ -67,7 +67,7 @@ public MessageBuffer next()
             return null;
         }
         b.flip();
-        return b.remaining() == 0 ? null : buffer.slice(0, b.limit());
+        return buffer.slice(0, b.limit());
     }
 
     @Override