Fix #79491: Search for .user.ini extends up to root dir

Fix #79491: Search for .user.ini extends up to root dir

The `start` parameter of `php_cgi_ini_activate_user_config` is supposed
to hold the byte offset of the doc root in the given `path`.  However,
the current expression which fixes a potential type incompatibility
will ever only evaluate to zero or one, because it uses the *logical*
and operator (`&&`).  Furthermore we notice that subtracting one from
`doc_root_len` is not necessary, so there is even no need for the
`start` parameter at all.