head: handle multibyte numeric utf-8 chars

src/uu/head/src/parse.rs

@@ -20,7 +20,7 @@ pub fn parse_obsolete(src: &str) -> Option<Result<impl Iterator<Item = OsString>
         let mut has_num = false;
         let mut last_char = 0 as char;
         for (n, c) in &mut chars {
-            if c.is_numeric() {
+            if c.is_digit(10) {
                 has_num = true;
                 num_end = n;
             } else {

tests/by-util/test_head.rs

@@ -306,6 +306,10 @@ fn test_head_invalid_num() {
                 ));
         }
     }
+    new_ucmd!()
+        .args(&["-c", "-³"])
+        .fails()
+        .stderr_is("head: invalid number of bytes: '³'");
 }
 
 #[test]