musl+gcompat error

[Conaclos]

Hi! I tried to use a rust crate that relies on pico-args using Alpine Linux (Musl-based distrib) and gcompat (glibc compatibility layer). I got the following error:

Message: removal index (is 0) should be < len (is 0)

at the following line: https://github.com/RazrFalcon/pico-args/blob/master/src/lib.rs#L127

It could be nice to add a defensive check and then removing the path only if it is present.