dvbepg: better support EPG data if lang is wrong

If multiple Digital TV devices are present, it is possible
that the languages available to be a different set. On such
case, if a language with non-exisiting data on some entries
is selected, instead of show empty strings, just get the
first language.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>