Concurrency checks are not validating subresources accesses correctly

[Cyphall]

Follow-up of the second issue reported in this message in issue #49.

I am getting a few "Potential race condition detected" between this write in the "cubemap generation" step and this read in the "mipmaps generation" step when processing an equirectangular skybox. I think the synchronization is good but maybe I'm wrong?

Initial diagnostic:

Currently, concurrency doesn't track at a per-subresource level. So it incorrectly marks it as a race condition.