test: add test for overflow in LineRange::from

src/line_range.rs

@@ -128,6 +128,13 @@ fn test_parse_plus() {
     assert_eq!(50, range.upper);
 }
 
+#[test]
+fn test_parse_plus_overflow() {
+    let range = LineRange::from("18446744073709551615:+1").expect("Shouldn't fail on test!");
+    assert_eq!(18446744073709551615, range.lower);
+    assert_eq!(18446744073709551615, range.upper);
+}
+
 #[test]
 fn test_parse_plus_fail() {
     let range = LineRange::from("40:+z");