`eszip extract` fails when a specifier in the eszip has no path or is a directory of another specifier

The code here:

https://github.com/denoland/eszip/blob/c9e9144ec617f2db50c011b42107969382c4f0fb/lib/eszip.ts#L89

...is very basic and looks at the pathname only to figure out how to extract.

This will fail in two scenarios:

1. Where there is no path, like `https://fresh.deno.dev`
2. A path is a directory of another specifier. For exmaple: `something/` then `something/other.ts`