// then update frame, frame1time (and possibly frame2, frame2time, lerpfrac)
// if set_times is not set, caller is responsible for frame1time, frame2time, csqcmodel_lerpfractime!
// then update frame, frame1time (and possibly frame2, frame2time, lerpfrac)
// if set_times is not set, caller is responsible for frame1time, frame2time, csqcmodel_lerpfractime!