libshine: fix support for shine 3.0

shine_encode_buffer expects written to be an int pointer, while the
previous shine_encode_frame expected it to be a long pointer.

Thus encoding with libshine currently always fails with
"internal buffer too small", because a negative return value of
shine_encode_buffer is interpreted as a very large long value.

Reviewed-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
