A branch of the "ends in a number checker" cannot be hit

[domenic]

What is the issue with the URL Standard?

https://url.spec.whatwg.org/#ends-in-a-number-checker

2. If the last item in parts is the empty string, then:

   1. If parts’s size is 1, then return false.

This can only be true if the input is the empty string. However, the empty string is never fed to the "ends in a number checker":

• https://url.spec.whatwg.org/#ref-for-ends-in-a-number-checker call site only feeds it the result of "domain to ASCII"
• https://url.spec.whatwg.org/#concept-domain-to-ascii asserts that the result is not the empty string before returning.

Transforming this branch into an assert might be good. Or, if we want to keep the "ends in a number checker" generic, maybe a note explaining this would be good.

(Found while working on jsdom/whatwg-url#268)

[annevk]

Nice find. I suggest we assert that parts's size is greater than 1.

I would also want to change step 4 to more clearly say "not the empty string".