Fixed PHP-1088: CID-10700: Explicit null dereferenced
Merge pull request #693 from bjori/PHP-1088-gridfs-coverity

Fixed PHP-1088: CID-10700: Explicit null dereferenced

* bjori/PHP-1088-gridfs-coverity:
  Fixed PHP-1088: CID-10700: Explicit null dereferenced
Fixed PHP-1090: Dereference null return value

Fixes several coverity issues around php_mongo_runcommand() retval changes
that was introduced by the fix for PHP-1036 (1831821f69d87f2ea0b7f0eb16ca8a750d4ecc85)