Fix a crash when running with FC_DEBUG=256

Fixes https://gitlab.freedesktop.org/fontconfig/fontconfig/issues/167
diff --git a/src/fcfreetype.c b/src/fcfreetype.c
index d528544..2f86d8a 100644
--- a/src/fcfreetype.c
+++ b/src/fcfreetype.c
@@ -1546,7 +1546,7 @@
 		    lang = FcSfntNameLanguage (&sname);
 
 		    if (FcDebug () & FC_DBG_SCANV)
-			printf ("%s\n", utf8);
+			printf ("%s\n", utf8 ? (char *)utf8 : "(null)");
 
 		    if (!utf8)
 			continue;