If a RunWorker fails to report success or failure (should not happen in
theory, but has been observed in practice, typically in exceptional code
paths) the RunControl will stay in 'Starting' or 'Stopping' state
forever. Give the user the opportunity to force a 'Stopped' state by a
second (or when 'Running' a third) time on the Stop button.

Change-Id: Iec58434927777bd67bfe01c5144ee5695b4d6cf1
Reviewed-by: Christian Stenger <christian.stenger@qt.io>