Black screen or artifacts appear when rendering a camera with an offset and scaled viewport (scissor rect) after the main camera.

Expected Result: The contents of the camera rendered after the main camera should appear in the correct viewport location.
Actual Result: Black screen or the correct viewport location but filled with noisy artifacts is rendered instead.

Steps to reproduce:

1) Open the attached project. Alternatively, use the VR functional test suite.
2) Go to Build settings > Player Settings > XR settings. Add Oculus and Cardboard sdk if building for GearVR or add Daydream if building for Daydream.
3) Build the project for GearVR/ Daydream with both scenes, "Start" and "Viewport" in the build settings.
4) Observe that a black screen is rendered for Viewport scene instead of the expected purple rectangle.

Reproducible on : 2018.1.0b9, 2018.1.0b1, 2018.1.0a7, 2017.3.0f3, 2017.2.0f2

Notes:
1) Works fine in Oculus. Fails in GearVR and Daydream.
2) 2017.1 doesn't have XR settings.