BC patch for breaking changes in PHP 7.2

The gettype() and get_resource_type() functions behave differently under PHP 7.2 - this patch provides backwards compatibility to ensure it doesn't break your tests. (a future major release might add the ability to indicate closed streams, but since this isn't possible on PHP < 7.2, we want consistent behavior on all PHP versions for the current release series; we might add this capability in a future, major release.)