**System Information**
Operating system: Windows-10-10.0.18362 64 Bits
Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 436.02
**Blender Version**
Broken: version: 2.81 (sub 15), branch: master, commit date: 2019-10-22 15:34, hash: `rBac18c3c28dee`
Broken: version: 2.80 (sub 75), branch: master, commit date: 2019-07-29 14:47, hash: `rBf6cb5f54494e`
Worked: version 2.79b, branch: master, commit date: 2018-03-22 14:10, hash: 'rBf4dc9f9d68b'
**Short description of error**
Undoing a completely cut hair with child particles enabled in particle edit mode crashes blender.
**Exact steps for others to reproduce the error**
Default factory startup.
1. Add a particle system
2. Change to hair
3. Enable interpolated children
4. Go into particle edit mode
5. Enable children
6. Switch to Cut and remove some of the hairs
7. Undo, crash.
{F7856517}