[zendframework/zf2#2633] Fix test failure
[zendframework/zf2#2633] Fix test failure

- Fix in zendframework/zf2#2633, while mostly correct, let $date with bool false value
  continue as valid, which it should not. Added another conditional,
  which ensures reported issue still is fixed, while keeping original
  behavior.

svycka/zend-validator,weierophinney/zend-validator,zendframework/zend-validator,akrabat/zend-validator,zf2timo/zend-validator,ezimuel/zend-validator,Maks3w/zend-validator