BacklogLimitExceeded exception removed

Hey guys! Thanks for developing this awesome library! 

Recently I have stumbled across a problem where I have a long running task, which updates it's progress every second. If that task runs for say 1567 seconds without any other code requesting to see it's progress, I get BacklogLimitExceeded exception on progress or result request. Second time I request for result it woks fine as it now has only 567 entries to parse. 

I made a workaround on my app which catches BacklogLimitExceeded exception and tries again until it gets to actual result, but that seems to me like it sounds - a workaround.

Dunno why you guys added that exception here, so here is my pull request to remove it. If it's necessary for some corner cases which I am not aware of, please share your knowledge on why it's needed. 

Thank you. Appreciate your work!