test: capture try_read panic on multi-byte input

Author: SAY-5

src/reader.rs

@@ -457,4 +457,15 @@ mod tests {
         assert_eq!(None, r.try_read());
         assert_eq!(None, r.try_read());
     }
+
+    #[test]
+    #[should_panic = "is_char_boundary"]
+    fn test_try_read_multibyte() {
+        let f = io::Cursor::new("\u{c3}");
+        let mut r = NBReader::new(f, Options::default());
+        let deadline = time::Instant::now() + time::Duration::from_secs(5);
+        while time::Instant::now() < deadline {
+            let _ = r.try_read();
+        }
+    }
 }