gitweb: avoid warnings for commits without body

In the unusual case when there is no commit message, gitweb would
output an uninitialized value warning.

Signed-off-by: Joey Hess <joey@kitenet.net>
Acked-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

gitweb/gitweb.perl

@@ -2092,7 +2092,7 @@ sub parse_commit_text {
 			last;
 		}
 	}
-	if ($co{'title'} eq "") {
+	if (! defined $co{'title'} || $co{'title'} eq "") {
 		$co{'title'} = $co{'title_short'} = '(no commit message)';
 	}
 	# remove added spaces