logging: Don't log empty byte buffers
logging: Don't log empty byte buffers

It could be that we're asked to log empty byte buffers. For instance the
payload of a "channel close" message from hyperstart is empty. Don't
emit a log entry in that case.

Signed-off-by: Damien Lespiau <64bd3cb94f359c1a3ce68dae5e26b40578526277@intel.com>

clearcontainers/proxy,clearcontainers/proxy