Spline IK and Auto-IK working together on the same bone chain could
crash due to the somewhat hacky way that they were sharing the same
list for the "iktree" forest. Resolved by doing what I should have
done from the beginning, and made Spline-IK save its ik chains off
into a separate list.
While this fixes the crash, it might be worth investigating outright
disabling this from working in this case, since it can be a bit
confusing to have it appear to not work.
2b6e4f2422