commit: loosen ident checks when generating template

commit: loosen ident checks when generating template

When we generate the commit-message template, we try to
report an author or committer ident that will be of interest
to the user: an author that does not match the committer, or
a committer that was auto-configured.

When doing so, if we encounter what we consider to be a
bogus ident, we immediately die. This is a bad idea, because
our use of the idents here is purely informational.  Any
ident rules should be enforced elsewhere, because commits
that do not invoke the editor will not even hit this code
path (e.g., "git commit -mfoo" would work, but "git commit"
would not). So at best, we are redundant with other checks,
and at worse, we actively prevent commits that should
otherwise be allowed.

We should therefore do the minimal parsing we can to get a
value and not do any validation (i.e., drop the call to
sane_ident_split()).

In theory we could notice when even our minimal parsing
fails to work, and do the sane thing for each check (e.g.,
if we have an author but can't parse the committer, assume
they are different and print the author). But we can
actually simplify this even further.

We know that the author and committer strings we are parsing
have been generated by us earlier in the program, and
therefore they must be parseable. We could just call
split_ident_line without even checking its return value,
knowing that it will put _something_ in the name/mail
fields. Of course, to protect ourselves against future
changes to the code, it makes sense to turn this into an
assert, so we are not surprised if our assumption fails.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>