Emit warning on IDN output failure

Warning is emitted before any dig headers.

bin/dig/dighost.c

@@ -4421,16 +4421,19 @@ idn_ace_to_locale(const char *src, char **dst) {
 	 */
 	res = idn2_to_unicode_8zlz(utf8_src, &local_src, 0);
 	if (res != IDN2_OK) {
-		/*
-		 * Cannot represent in current locale.
-		 * Output ACE form undecoded.
-		 */
+		static bool warned = false;
+
 		res = idn2_to_ascii_8z(utf8_src, &local_src, 0);
 		if (res != IDN2_OK) {
 			fatal("Cannot represent '%s' "
 			      "in the current locale nor ascii (%s), "
 			      "use +noidnout or a different locale",
 			      src, idn2_strerror(res));
+		} else if (!warned) {
+			fprintf(stderr, ";; Warning: cannot represent '%s' "
+			      "in the current locale",
+			      local_src);
+			warned = true;
 		}
 	}