gitweb: Fix errors in git_patchset_body for empty patches

gitweb: Fix errors in git_patchset_body for empty patches

We now do not skip over empty patches in git_patchset_body (where
empty means that they consist only of git diff header, and of extended
diff header, for example "pure rename" patch).  This means that after
extended diff header there can be next patch (i.e. /^diff /) or end of
patchset, and not necessary patch body (i.e. /^--- /).

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