How to reproduce:
1. Open Unity
2. Load tester-submitted project(TesselationTest.zip)
3. Open '1.unity' scene
4. Select 'New Material' in 'Project view'
5. Increase 'Max Tessellation' attribute
6. If Unity did not crash, close Unity(while tessellation attribute is set to 20 < number) and repeat steps 1-5

Expected result: Distance-based Tessellation function can work with changing values(between frames)
Actual result: Distance-based tessellation function crashes unity

Notes:
* Edge length based tessellation won't crash Unity in the same scenario
* This crash can also be easily reproduced on user-submitted project
* This crash can also be triggered changing tessellation distance parameters

Reproducible with - 2017.1.3p2, 2017.2.2p1, 2017.3.1p4, 2018.1.0a1, 2018.1.0b10. 2018.2.0a1, 2018.2.0a2
Not reproducible with - 5.6.4p4, 2018.1.0b11, 2018.2.0a3, 2018.2.0a4

Verified in: 2018.1.0b11, 2018.2.0a3