Is there a law that says you cannot defend your life while committing a nonviolent crime?

Yes, 939.48(1m)(b)1

(b) The presumption described in par. (ar) does not apply if any of the following applies:
1. The actor was engaged in a criminal activity or was using his or her dwelling, motor vehicle, or place of business to further a criminal activity at the time.

Moreover, if reports are to be believed, provocation also removes the protection per subsection (2)(a):

A person who engages in unlawful conduct of a type likely to provoke others to attack him or her and thereby does provoke an attack is not entitled to claim the privilege of self-defense against such attack, except when the attack which ensues is of a type causing the person engaging in the unlawful conduct to reasonably believe that he or she is in imminent danger of death or great bodily harm. In such a case, the person engaging in the unlawful conduct is privileged to act in self-defense, but the person is not privileged to resort to the use of force intended or likely to cause death to the person's assailant unless the person reasonably believes he or she has exhausted every other reasonable means to escape from or otherwise avoid death or great bodily harm at the hands of his or her assailant.