merge_pmt_versions was not usable if multiple programs were present because
when it was searching for candidate streams it did not make sure that the PMT was
of the same program. This caused the streams of all programs to get merged into
a single (garbled) program.

This patch makes sure that the program number (service ID) is also matching
with the old streams when parsing the PMT making the feature useful for multi
program streams.

This change might cause issues for single program streams if the program number
changes, but I think it is acceptable because the goal of the option is to make
the parsing resilient to PID changes, and that is still working as expected.
Signed-off-by: Marton Balint <cus@passwd.hu>