Do not call reinterpret_cast when converting from NULL.

Do not call reinterpret_cast when converting from NULL.

If NULL is a nullptr (such as on my FreeBSD system), it is not possible to
use reinterpret_cast to convert it to another pointer. Plus, just using NULL
directly achieves the same effect.

R=ulan@chromium.org

Review URL: https://chromiumcodereview.appspot.com/19388005

Patch from Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15705 ce2b1a6d-e550-0410-aec6-3dcde31c8c00