Module URL with no trailing slash has broken links

[rsp]

Example:

• https://deno.land/x/dirname/ (with slash)
  • mod.ts links to https://deno.land/x/dirname/mod.ts (good)
• https://deno.land/x/dirname (without slash)
  • mod.ts links to https://deno.land/x/mod.ts (bad)

Additionally, the effect of a bad link is a blank screen with no 404 error or any other message.

Example:

• https://deno.land/x/nonexistent/path/name

Expected result: 404 error

What is visible: A quick flash of a header and a blank screen.