Feature Request: Skip all calculations if nothing emitted in a domain

[kentbarber]

If there has been no particles or volume data emitted into a volume then onAdvanceTimeStep could immediately return.

This should be optional, perhaps with a flag that can be set. Since in some cases you might want forces to be present and being simulated before you emit. But in my case I am looking at only starting calls to the solver->update() method when a volume has data, which I thought could be handled internally instead of checking for collisions ( in my case of a moving emitter through a domain).

[doyubkim]

Thanks for the suggestion! Will think about it as an optimization.