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/InputFilter.cpp

@@ -347,7 +347,7 @@ bool InputFilter::IsBeingPressed( const DeviceInput &di, const DeviceInputList *
 	if( pButtonState == NULL )
 		pButtonState = &g_CurrentState;
 	const DeviceInput *pDI = FindItemBinarySearch( pButtonState->begin(), pButtonState->end(), di );
-	return pDI != NULL && pDI->bDown;
+	return pDI != nullptr && pDI->bDown;
 }
 
 float InputFilter::GetSecsHeld( const DeviceInput &di, const DeviceInputList *pButtonState ) const