Fixed PHP-1036: Segmentation Fault when querying large collection and the working set is not loaded
Fix similar issues as PHP-1036 by verifying if we actually have a zval before trying to
return it. mongo_rucommand() will throw an exception if its null, so no need to else RETURN_NULL()
Merge pull request #668 from bjori/PHP-1036-distinct-segfault

Php 1036 distinct segfault

* bjori/PHP-1036-distinct-segfault:
  Fix similar issues as PHP-1036 by verifying if we actually have a zval before trying to return it. mongo_rucommand() will throw an exception if its null, so no need to else RETURN_NULL()
  Fixed PHP-1036: Segmentation Fault when querying large collection and the working set is not loaded