Update to perhaps fix crash when cancelling stream requests.
Update to perhaps fix crash when cancelling stream requests.

The streaming requests code needs to be refactored into a stand-alone
class to reduce the details in the world model server and abstract out
annoying things, like locks.

  modified:   wmserver/world_model_server.cpp

OwlPlatform/world-model,OwlPlatform/world-model,OwlPlatform/world-model