Downsampled SceneColour textures are not invalidated after ComposeToNewSceneColor when TSR is enabled leading to AfterMotionBlur materials not rendering bloom

When an emissive AfterMotionBlur material is used with TSR, Bloom is not applied to the material.

The cause for this appears to be that AfterMotionBlur materials are composed to a separate texture in PostProcessing.cpp:1102. On line 1112, there is a check that causes invalidation of the downsampled textures that TSR has already generated. This condition is not met when TSR is enabled, leading to the Bloom pass operating on the unmodified, non-composited TSR HalfRes texture.

1. Create an emissive AfterMotionBlur material
2. Place in level
3. Switch AA mode from 4 (TSR) to 2 (TAA) and back.

Observed: the bloom from the emissive is absent in the TSR view
Expected: the same bloom between TAA and TSR