`url_to_postid` can fail in some contexts due to `set_url_scheme`

[batmoo]

This is a follow-up to #34144.

The set_url_scheme addition breaks the use of url_to_postid when there is a mismatch between the current scheme and the scheme of the home_url.

Example: In a multisite environment, I have two blogs: insecure.example.com and secure.example.com. Only secure.example.com has https enabled and we force home_url for insecure.example.com to always return an http URL.

The following will fail if called from ​https://secure.example.com:

switch_to_blog( 2 ); // insecure.example.com
$post_id = url_to_postid( 'http://insecure.example.com/2016/01/01/hello/' );
restore_current_blog();

This is because set_url_scheme forces the permalink to have an https scheme but the bit of code in url_to_postid that strips the home_url() form the URL will fail because of the scheme mismatch.

I think the better fix would be to make sure that the set_url_scheme call matches the scheme of home_url.

[ocean90]

@swissspidy Can you take a look at this?

[johnbillion]

In 36750:

Rewrite Rules: Ensure url_to_postid() operates as expected when it's used in the context of another site within a Multisite network that uses mixed URL schemes.

Fixes #35531