Answer:
We can say that Pat is liable to Tom for the loss of the bike.
Explanation:
When an object is borrowed to someone, this means the object has to be returned to the owner. The person who has borrowed the object is responsable to return it. Whatever happends inbetween, before or after doesn´t give away the responsability of what happends to that object.
Responsability is a matter in this case. When Pat asked if he can use the bike, he automatically asumed a responsability to return it and to take care of it.
Pat did not lock the bike when he left it in his porch, so one can say that even if this must definetly ocurred without intentionality. He is still responsable for the object lend.