OSSL_STORE "file" scheme loader: check for absolute path in URI later

If we have a local file with a name starting with 'file:', we don't
want to check if the part after 'file:' is absolute.  Instead, mark
each possibility for absolute check if needed, and perform the
absolute check later on, when checking each actual path.

Reviewed-by: Andy Polyakov <appro@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3907)