// check if the given co-ordinates are inside an inset at the
// given cursor, if one exists. If so, the inset is returned,
// and the co-ordinates are made relative. Otherwise, 0 is returned.
// check if the given co-ordinates are inside an inset at the
// given cursor, if one exists. If so, the inset is returned,
// and the co-ordinates are made relative. Otherwise, 0 is returned.