name-rev: restructure parsing commits and applying date cutoff

name-rev: restructure parsing commits and applying date cutoff

At the beginning of the recursive name_rev() function it parses the
commit it got as parameter, and returns early if the commit is older
than a cutoff limit.

Restructure this so the caller parses the commit and checks its date,
and doesn't invoke name_rev() if the commit to be passed as parameter
is older than the cutoff, i.e. both name_ref() before calling
name_rev() and name_rev() itself as it iterates over the parent
commits.

This makes eliminating the recursion a bit easier to follow, and the
condition moved to name_ref() will be moved back to name_rev() after
the recursion is eliminated.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>