gitweb: Fix thinko in git_tags and git_heads

git_get_refs_list always return reference to list (and reference to
hash which we ignore), so $taglist (in git_tags) and $headlist (in
git_heads) are always defined, but @$taglist / @$headlist might be
empty. Replaced incorrect "if (defined @$taglist)" with
"if (@$taglist)" in git_tags and respectively in git_heads.

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

gitweb/gitweb.perl

@@ -2576,7 +2576,7 @@ sub git_tags {
 	git_print_header_div('summary', $project);
 
 	my ($taglist) = git_get_refs_list("tags");
-	if (defined @$taglist) {
+	if (@$taglist) {
 		git_tags_body($taglist);
 	}
 	git_footer_html();
@@ -2589,7 +2589,7 @@ sub git_heads {
 	git_print_header_div('summary', $project);
 
 	my ($headlist) = git_get_refs_list("heads");
-	if (defined @$headlist) {
+	if (@$headlist) {
 		git_heads_body($headlist, $head);
 	}
 	git_footer_html();