Steps to reproduce:
1. Open attached project
2. Open SampleScene
3. Enter Play mode
4. Notice that the main camera viewport changes from 0.5 to 1 every few seconds

Expected result: The main camera viewport content should be green to the left and white everywhere else (no red)
Actual result: When then main camera viewport height is 0.5, a red quad appears on the right

Reproducible with: 2017.4.32f1, 2018.4.10f1, 2019.1.14f1, 2019.2.7f2, 2019.3.0b5, 2020.1.0a6

Notes:
- The red quad should never be visible and should always fail the Z test since the code clears the depth buffer at 0.5. This shouldn't depend on the viewport width/height/location