Approximately three or four times now, the issue of pointers being
in an inconsistent state been an issue in the video backend renderers
with regards to tripping up other developers.
Global (ugh) resources are put into a unique_ptr and will always have a
well-defined state of being - null or not null
The usual way to handle this kind of request is to rise a flag which the gpu thread polls.
The gpu thread itself either generates the result or just write zeros if disabled.
After this, it rise another flag which says that this work is done.
So if disabled, we still have the cpu-gpu round trip time. This commit just returns 0 on the cpu thread
instead of playing ping pong...
