Added timeout non-zero verification - fixes #776

The pubsub listener was making the `bstop` call wait forever, because it was never listening in the first place: the 0 second `Duration` timeout was being triggered, rather than being considered as a "no timeout" value.
@etcimon: The blame is on the build box, I think. It looks like compiling the example uses up too much RAM and the compiler process gets killed. The Redis test is the only example that defines an additional "RedisDebug" version (and thus causes vibe.d to be compiled again) and removing that from the checked in dub.json would fix the issue.