It seems that the current code fails to delete softBody in sync with recalculating mechanical constraints. This leads to an assertion fail in Eigen. This patch delays constraints recalculation and sometimes saves Step from crashing.

Any help in triagging the crash and improving this patch will be much appreciated.

https://bugs.kde.org/show_bug.cgi?id=408574

BUG: 408574

1. Start Step.
2. Add soft body.
3. Add a stick which starts or ends on any of the soft body particles (to trigger the snapping to this particle).
4. Delete the soft body using "World" dock or by selecting it and pressing the 'Delete' key.
5. Step does not crash anymore if one of the stick ends is then moved. However, it crashes if you move the stick as a whole.