Bug 1113574 - Check that the room <chatbox> is still open before resuming the tour from a join notification. r=dmose,markh

The room participant list only gets updated after getting a push notification and this can lead to the Rooms store still showing the user in their room even after they have left. To avoid this, we check that the <chatbox> for the room is actually still present.

--HG--
extra : rebase_source : f4133b922e8be4cc3ece3aebc9e96162efd3190e