Posthoc does not handle when workers crash (presents as infinite loading)

[spaaaacccee]

When a web worker crashes, the main thread does not get informed of this, and as such keeps waiting for the worker to return. This is problematic when loading traces cause the parser worker to crash. When a web worker crashes, this event should be handled by the main thread.

[dharabor]

This or a very similar issue currently affects the StarCraft example, on Firefox. Steps to reproduce: after first load, disable all layers except "Walk". The app goes into an infinite"loading" state.