gitweb: use Perl built-in utf8 function for UTF-8 decoding.

Signed-off-by: Nİsmail Dönmez <ismail@pardus.org.tr>
Tested-by: NMartin Koegler <mkoegler@auto.tuwien.ac.at>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

gitweb/gitweb.perl

@@ -695,10 +695,9 @@ sub validate_refname {
 # in utf-8 thanks to "binmode STDOUT, ':utf8'" at beginning
 sub to_utf8 {
 	my $str = shift;
-	my $res;
-	eval { $res = decode_utf8($str, Encode::FB_CROAK); };
-	if (defined $res) {
-		return $res;
+	if (utf8::valid($str)) {
+		utf8::decode($str);
+		return $str;
 	} else {
 		return decode($fallback_encoding, $str, Encode::FB_DEFAULT);
 	}