3D model became corrupted when the editor was attempted to be closed during probuilder subdivision task.

2. How we can reproduce it using the example you attached

1) Create a new cube using probuilder.
2) Subdivide it until unity is unresponsive due to the processing
3) Attempt to close unity while it is unresponsive by using the red 'X' button in the top right of the window
4) When unity asks if you want to save, press cancel
5) Ta-Da! Your cube is corrupted (should look like in the attached video)

Reproduced in: 2018.1f1, 2018.1f2 , Version 2018.3.0a1 (c7051b83ff4b)
Package version: 2.9.8f3, 3.0.0, 3.0.8

Bug report courtesy of Milton Jenney (Work experience)