gitweb: Fix export check in git_get_projects_list

When $filter was empty, the path passed to check_export_ok would
contain an extra '/', which some implementations of export_auth_hook
are sensitive to.

It makes more sense to fix this here than to handle the special case
in each implementation of export_auth_hook.

Signed-off-by: Devin Doucette <devin@doucette.cc>
Acked-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

gitweb/gitweb.perl

diff --git a/gitweb/gitweb.perl b/gitweb/gitweb.perl
index 8f574c7..99f71b4 100755
--- a/gitweb/gitweb.perl
+++ b/gitweb/gitweb.perl
@@ -2147,8 +2147,9 @@
 
 				my $subdir = substr($File::Find::name, $pfxlen + 1);
 				# we check related file in $projectroot
-				if (check_export_ok("$projectroot/$filter/$subdir")) {
-					push @list, { path => ($filter ? "$filter/" : '') . $subdir };
+				my $path = ($filter ? "$filter/" : '') . $subdir;
+				if (check_export_ok("$projectroot/$path")) {
+					push @list, { path => $path };
 					$File::Find::prune = 1;
 				}
 			},