Fix: avoid prime worker message spam.

[dvogel]

The prime worker can receive messages posted by browser extensions (e.g. react-devtools-bridge). Since the message lacked the necessary inputs, the prime algorithm would start but never terminate. This drops useless messages on the floor.

[davidlehn]

I'm not sure what to do with this.

On one hand, I can see how getting arbitrary messages could cause problems. And I can see how this is a simple change that would fix it (other than in the edge case where the arbitrary message had the same fields).

On the other hand, I can't see why a browser extension would send arbitrary messages to a worker and not expect havoc to ensue. What is being sent, and why?

Is there somewhere that suggests best practices for this?

[dlongley]

I think it's fine to ensure that we're only acting on messages that are intended to be received by the worker. However, we should add a more specific message type property (with a value that is an identifier that specifies the message is a forge prime worker message) that we can check rather than relying on looking for e.data.hex and e.data.workLoad.

[davidlehn]

Tried another approach in #941.

[dlongley]

Closing in favor of #941, which should be merged.