stty: fix: reject "+hex" in parse_saved_state

Author: Rudxain

src/uu/stty/src/stty.rs

@@ -524,9 +524,15 @@ fn parse_saved_state(arg: &str) -> Option<Vec<u32>> {
     // Validate all parts are non-empty valid hex
     let mut values = Vec::with_capacity(expected_parts);
     for (i, part) in parts.iter().enumerate() {
+        // `from_str_radix` doesn't document its behavior for this case,
+        // thus, we do this to guarantee stability
         if part.is_empty() {
             return None; // GNU rejects empty hex values
         }
+        // TO-DO: avoid `from_str_radix`
+        if part.as_bytes()[0] == b'+' {
+            return None;
+        }
         let val = u32::from_str_radix(part, 16).ok()?;
 
         // Control characters (indices 4+) must fit in u8