[media] dvb_demux: Transport stream continuity check fix

This patch avoids incrementing continuity counter
demux->cnt_storage[pid] for TS packets without payload in accordance
with ISO /IEC 13818-1.

[mchehab@redhat.com: unmangle whitespacing and fix CodingStyle.
 Also checked ISO/IEC spec: patch is according with it]
Reviewed-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: John Smith <johns90812@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>