The big NULL replacement party part 1.

This is meant to be a safer alternative since
NULL can often be 0. Let's not rely on that.

And yes, I know this is a lot of files. This is
a safer thing to do in big commits vs for loops.

src/GameLoop.cpp

@@ -281,7 +281,7 @@ void ConcurrentRenderer::Stop()
 
 void ConcurrentRenderer::RenderThread()
 {
-	ASSERT( SCREENMAN != NULL );
+	ASSERT( SCREENMAN != nullptr );
 
 	while( !m_bShutdown )
 	{