Fix for AccessViolation on Windows 8.1 x64

This is a fix for an error that was happening on Windows 8.1 x64.
I do not want to break any good behavior, but this fixed the problem.

This is the issue : 
https://github.com/tmyroadctfig/twaindotnet/issues/10#issuecomment-60686610%3E%20.%20%3Chttps://github.com/notifications/beacon/AI4_jmUi9RJWk4D9umgU9PAkiHzxVGb7ks5nHso5gaJpZM4BRfTT.gif

Please review it. Thank you!