Fix viewport rendering when displaying as byte and not half float
Fix viewport rendering when displaying as byte and not half float

Commit rB7e61e597253f3ca75f2fb86a57212ca750ffbbe8 broke viewport rendering when not displaying as halfs.
This fixes that by actually using the `scale` parameter that is passed into `film_map` and also de-duplicates code around it.

Differential Revision: https://developer.blender.org/D6557

tangent-opensource/coreBlackbird,tangent-opensource/coreBlackbird,tangent-opensource/coreBlackbird