-l command line argument (redux)

I cannot reopen a bug but it looks #565 is still not solved as of 0.28.0.

I just retested and it's still just as buggy as before:

> I can confirm the issue with yapf 0.21.0:
>
> ```
> % cat -n /tmp/id.py
> 1 a = {1:
> 2 2, 3:4}
> 3
> 4 # hello
> 5
> 6
> % yapf -d -l 1-2 /tmp/id.py
> --- /tmp/id.py (original)
> +++ /tmp/id.py (reformatted)
> @@ -1,6 +1,3 @@
> -a = {1:
> -2, 3:4}
> +a = {1: 2, 3: 4}
>
> # hello
> -
> -
> ```
>
> yapf is told to reformat only lines 1 to 2 but it removes blank lines 5 and 6 which are clearly out of the specified range.
>
> The `-l` argument handling seems very buggy, please fix it.

The lines 1-2 are not selected and so should not be reformatted, but yapf insists on doing it