printf: add error handling to escaped unicode characters

tests/by-util/test_printf.rs

@@ -112,6 +112,26 @@ fn escaped_unicode_null_byte() {
         .stdout_is_bytes([1u8, b'_']);
 }
 
+#[test]
+fn escaped_unicode_incomplete() {
+    for arg in ["\\u", "\\U", "\\uabc", "\\Uabcd"] {
+        new_ucmd!()
+            .arg(arg)
+            .fails_with_code(1)
+            .stderr_only("printf: missing hexadecimal number in escape\n");
+    }
+}
+
+#[test]
+fn escaped_unicode_invalid() {
+    for arg in ["\\ud9d0", "\\U0000D8F9"] {
+        new_ucmd!().arg(arg).fails_with_code(1).stderr_only(format!(
+            "printf: invalid universal character name {}\n",
+            arg
+        ));
+    }
+}
+
 #[test]
 fn escaped_percent_sign() {
     new_ucmd!()