gitweb: skip unreadable subdirectories

gitweb terminates and shows no project list, if it can not access a
sub-directory in the project root directory while looking for projects
to show.

Work it around by skipping unreadable directories.

Signed-off-by: Hielke Christian Braun <hcb@unco.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

gitweb/gitweb.perl

@@ -3071,6 +3071,8 @@ sub git_get_projects_list {
 				return if (m!^[/.]$!);
 				# only directories can be git repositories
 				return unless (-d $_);
+				# need search permission
+				return unless (-x $_);
 				# don't traverse too deep (Find is super slow on os x)
 				# $project_maxdepth excludes depth of $projectroot
 				if (($File::Find::name =~ tr!/!!) - $pfxdepth > $project_maxdepth) {