parse: fuzzing errors

[0x61nas]

I just ran the fazzer on the parse method and it found some panics, which may be interested in.

ws:

x
n--

x
n--

-

The minimized cases:

``` ws: xn--xn-- - ``` ``` ws: x n--x n-- - ``` ``` ws: x n--x n-- - ``` ``` ws: xn--x n-- - ``` ``` ws:xn--xn--- ```