Unbreak databases/php72-mysqli when lang/php72 is build with MYSQLND=off

Currently when building lang/php72 with MYSQLND=off, its im possible to
build databases/php72-mysqli. When the option MYSQLND was added, we expected
users to not use mysqli at all after disabling this option.
This has proven to be wrong, so we patch the build to be work again.

patch-ext_mysqli_mysqli__api.c was submitted by Сергей <joker@pinnet.ru>.