Scene View Extension - Subscribing to Tonemap's afterpass renders black screen

Callbacks for the Tonemap's afterpass that return identity return black screen unless there is a post-process material.

1. Download attached repro project
2. Compile, open project.
3. Run PIE, observe black screen
4. Add PostProcessVolume (unbounded) and add an identity Post-Process material. Run PIE again, observe scene rendering normally.