Blender Git Loki

Fix for shifted sample-to-frame mapping in Alembic files with hair
simulation.

The hair sim skips the first frame (velocities are undefined there), but
still has to create the motion state data in order to have it written
as a sample. Otherwise the strands motion state samples start one sample
short and frames get mapped to one sample in the past. This then leads
to incorrect movement of all hair vertices other than the roots (which
are always clamped to the animated positions).