SPRINGFIELD — Drivers who cause car crashes while on drugs may have a new way to defend themselves against criminal charges.The state’s top court ruled this morning in a 5-2 decision that defendants in such cases can use the so-called “act of God” defense, a civil law concept in which an incident is deemed unforeseeable or beyond prevention.But while ruling that a woman who caused a crash with cannabis in her system should have been allowed to argue the incident was due to a medical emergency, the …