Fix building with Clang.

* Return NULL for function with return type "void *".
Fix for CVE-2012-0722, patch provided by Sajjad Pourali http://www.securation.com/
Merge pull request #66 from manphiz/clang-build-fix

Fix building with Clang.
Merge pull request #68 from LocutusOfBorg/master

Fix for CVE-2012-0722, patch provided by Sajjad Pourali