Allow empty authority for unknown schemes

[jfinkhaeuser]

I discussed this briefly with @bagder

According to RFC3986 Section 3.2.2 on page 21

If the URI scheme defines a default for host, then that default
applies when the host subcomponent is undefined or when the
registered name is empty (zero length). For example, the "file" URI
scheme is defined so that no authority, an empty host, and
"localhost" all mean the end-user's machine, whereas the "http"
scheme considers a missing authority or empty host invalid.

cURL implements this behaviour for the file scheme, but doesn't - and cannot - implement this behaviour for schemes it does not know. For such schemes, passing a new flag that permits empty authority sections is desirable.

This PR adds such a CURLU_NO_AUTHORITY flag, as well as test cases.

[jfinkhaeuser]

I've got to run - if there are tests failing, or there should be changes, I'll look at them in a few days, probably. Locally everything looked fine. And obviously if you'd like changes, I'm happy to provide them.

[bagder]

I think this is a sensible way to make the parser handle such URLs so I'm in favor of merging once things are green. Still missing: documentation of the new flag and symbols-in-versions update.

[jfinkhaeuser]

Makes sense - will probably get to those changes tomorrow.

[bagder]

The two builds using boringssl fail due to other reasons, not your fault!

[jfinkhaeuser]

Excellent, then let me know if you want any other changes, otherwise I'm done.

[bagder]

Will merge asap!

[bagder]

Thanks!

[jfinkhaeuser]

No worries, glad to be of help!