gitweb: fix project list if PATH_INFO=="/".

The project list now uses several common header / footer generation functions.
These functions only check for "defined $project", but when PATH_INFO just
contains a "/" (which is often generated by web servers), then this test
fails.

Now explicitly undef $project if there is none so that the tests in other
gitweb parts work again.

Signed-off-by: Martin Waitz <tali@admingilde.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

gitweb/gitweb.perl

@@ -95,8 +95,9 @@
 if (defined $project) {
 	$project =~ s|^/||;
 	$project =~ s|/$||;
+	$project = undef unless $project;
 }
-if (defined $project && $project) {
+if (defined $project) {
 	if (!validate_input($project)) {
 		die_error(undef, "Invalid project parameter");
 	}