Fix erroneous cast from byte to int in IBBInputStream's read()
method. The casted value needs to be masked with 0xff, because bytes
in java are signed (two's complement)

Fixes SMACK-394

git-svn-id: https://svn.igniterealtime.org/svn/repos/smack/trunk@13387 b35dd754-fafc-0310-a699-88a17e54d16e