Disallow incorrect wrapping range expression for --nth

src/tokenizer.go

@@ -73,7 +73,7 @@ func ParseRange(str *string) (Range, bool) {
 		}
 		begin, err1 := strconv.Atoi(ns[0])
 		end, err2 := strconv.Atoi(ns[1])
-		if err1 != nil || err2 != nil || begin == 0 || end == 0 {
+		if err1 != nil || err2 != nil || begin == 0 || end == 0 || begin < 0 && end > 0 {
 			return Range{}, false
 		}
 		return newRange(begin, end), true

src/tokenizer_test.go

@@ -40,6 +40,18 @@ func TestParseRange(t *testing.T) {
 			t.Errorf("%v", r)
 		}
 	}
+	{
+		i := "1..3..5"
+		if r, ok := ParseRange(&i); ok {
+			t.Errorf("%v", r)
+		}
+	}
+	{
+		i := "-3..3"
+		if r, ok := ParseRange(&i); ok {
+			t.Errorf("%v", r)
+		}
+	}
 }
 
 func TestTokenize(t *testing.T) {