gitweb: Fix error in git_patchest_body for file creation/deletion patch

gitweb: Fix error in git_patchest_body for file creation/deletion patch

$from_id, $to_id variables should be local per PATCH.

Fix error in git_patchset_body for file creation (deletion) patches,
where instead of /dev/null as from-file (to-file) diff header line, it
had link to previous file with current file name.  This error occured
only if there was another patch before file creation (deletion) patch.

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>