Properly continue match after pathless routes

[taion]

Fixes #3307

[taion]

I think this issue only comes up with a splat nested under pathless routes.

This is a simplified version of a fix from #3246.

[taion]

Just to explain what's happening with these in a bit more detail – to actually avoid matching extraneous slashes per #3158, we need to be careful about whether the slash ends up in the "remaining pathname" after a match, or if it ends up consumed by the match pattern itself.

Normally this isn't a problem, but there's an edge case with pathless routes when the pathname is /, such that the pathless routes will incorrectly "consume" the slash.

The more complicated fix in #3246 "restores" the slash, but it's easier (and cheaper) to just not run the match in the first place, since we know it's not going to accomplish anything.

[taion]

Could I get a review here? I'd like to cut a release to address @MoOx's issue.

[taion]

Thanks!