afs: Provide generic counter for matching rows.

afs: Provide generic counter for matching rows.

Several afs commands implemented their own counters, often only to
find out whether they should print an error message because no rows
matched the given pattern(s).

This patch makes counting matching rows generic by increasing the new
pattern_match_data->num_matches counter in action_if_pattern_matches()
so that all commands which use this facility for iterating over all
audio files can evaluate the counter afterwards. This allows to remove
several per-command counters.