bodyfetcher.py: give up if post doesn't have data
bodyfetcher.py: give up if post doesn't have data

Recent ValueError failures from attempting to decode JSON which
wasn't there, apparently because SO is now killing off hung sockets
after a timeout.

Charcoal-SE/SmokeDetector,Charcoal-SE/SmokeDetector,ArtOfCode-/SmokeDetector,ArtOfCode-/SmokeDetector