The use of force, but not deadly force, against a mental incompetent is justified:
(1) if the actor is the incompetent's guardian or someone similarly responsible for the general care and supervision of the incompetent; and
(2) when and to the degree the actor reasonably believes the force is necessary:
(A) to safeguard and promote the incompetent's welfare; or
(B) if the incompetent is in an institution for his care and custody, to maintain discipline in the institution.