'Fix' pointer dereference error in vugen with dummy function

This is a rather interesting problem that only occurs if you have y_transaction.c in a script without using lr_start_transaction() or lr_end_transaction anywhere. This can happen if you only use ylib, and nothing else.

The error you get running such a script is a popup complaining about a dereference going wrong.
Add a lr_start_transaction() and a lr_end_transaction() call into a dummy function anywhere though .. poof, no error.