[php-src] Issue #7894: filter_var("false", FILTER_VALIDATE_BOOL returns the set default value

Issue: https://github.com/php/php-src/issues/7894 Comment Author: TobiGr I am sorry to bother you again, but I looked deeper into the issue and still got return values which I do not expect. ``` php var_dump(filter_var(null, FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE)); var_dump(filter_var(null, FILTER_VALIDATE_BOOLEAN, ['options' => ['default' => 2], 'flags' => FILTER_NULL_ON_FAILURE])); ``` results in ``` bool(false) bool(false) ``` although the docs say > If FILTER_NULL_ON_FAILURE is set, false is returned only for "0", "false", > "off", "no", and "", and null is > returned for all non-boolean values.