Fixes#741
The current code will skip `deserializePayloadIfNecessary` if the
payload is a `byte[]`. There are in fact two conditions that indicate
that a message does not require postprocessing in the binder: that
the payload is not a `byte[]` which indicates that the message has
already been deserialized, and that the `originalContentType` is not
present, or else it'd need to be moved to `contentType`. This fix
adds the secondary condition to the check.
4d74212932