Fix for issue when file or directory name is "0"

Summary: If name of file or directory is `0` - this name shouldn't be removed in `::resolveDotDots` method.
Solution is to use `strlen` function as callback in `array_filter` - it will works similarly, but keeps values of 0 (zero).

Likely, should be backported into 3.3 LTS branch (I can add another pull request against 3.3 branch if this is OK).
Closes https://github.com/facebook/hhvm/pull/4266

Reviewed By: @fredemmott

Differential Revision: D1687469

Signature: t1:1687469:1417307697:14f3413565305ff2289b271c91b188c28bdc688f