Fix error when parsing hex value with non-ASCII

[5225225]

Previously, the string slicing below would panic because they hit invalid UTF8 characters

[5225225]

Is there anything I can do to help get this merged @mazznoer ?

I'm fuzzing https://github.com/wez/wezterm's escape parser, and am running into this panic, since it uses csscolorparser::parse. I'm assuming it can be mitigated against with some checks on wezterm's end, but would be good to not have anyone else run into this.

[wez]

wezterm/wezterm@a22942a works around this issue in the meantime