gitweb: Simplify snapshot format detection logic in evaluate_path_info

gitweb: Simplify snapshot format detection logic in evaluate_path_info

This issue was caught by perlcritic in harsh severity level noticing
that catch variable was used outside conditional thanks to the
Perl::Critic::Policy::RegularExpressions::ProhibitCaptureWithoutTest
policy.  See "Perl Best Practices", chapter 12. Regular Expressions,
section 12.15. Captured Values:

   Pattern matches that fail never assign anything to $1, $2, etc.,
   nor do they leave those variables undefined. After an unsuccessful
   pattern match, the numeric capture variables remain exactly as they
   were before the match was attempted.

New version is in my opinion much easier to understand; previous
version worked correctly due to the fact that we returned from loop
on first found match.

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Acked-by: Giuseppe Bilotta <giuseppe.bilotta@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>