Dispatch incoming_call synchronously
Dispatch incoming_call synchronously

- this should fix a race where if the 'hangup' arrives hard on the tail of the
Call.incoming, we don't ignore it.

(We still have a problem in that we blip the hangup tone and UI, but that is
arguably a separate problem)

matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,aperezdc/matrix-react-sdk,aperezdc/matrix-react-sdk,matrix-org/matrix-react-sdk,aperezdc/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,aperezdc/matrix-react-sdk,matrix-org/matrix-react-sdk