match_pathname(): reorder prefix-match check

match_pathname(): reorder prefix-match check

As an optimization, we use fspathncmp() to match a prefix of the pattern
that does not contain any wildcards, and then pass the remainder to
fnmatch(). If it has matched the whole thing, we can return early.

Let's shift this early-return check to before we tweak the pattern and
name strings. That will gives us more flexibility with that tweaking.

It might also save a few instructions, but I couldn't measure any
improvement in doing so (and I wouldn't be surprised if an optimizing
compiler could figure that out itself).

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