4266538ab9
This was caused by strips with single frame input like single image strip or color strip. their length is always 1, and so content length was calculated to end after first frame. There was code handling this case, but it was also checking for `anim_endofs` and `endstill` values. Anim offset values have no effect on these strips and still frame value was used incorrectly. So these chacks can be removed completely.