Steps to repro:

1. Open Unity;
2. Open attached project and 'test' scene;
3. Launch the scene.

Actual result:
'Assertion failed on expression: 'desc.fadeData[i].transitionDistance > 0' '
error is shown in the console. The issue happens when crossfade animation is tuned off and Billboard LOD level is set to 100% on SpeedTree model.

Expected result:
Assertion should not be shown when toggling SpeedTree settings.

Notes:
- Reproducible in 5.6.0a2, 5.5.0b11, 5.4.2p2;
- Reproducible on Windows 10 and OS X 10.11.2.