debugger: fix problem where a manual 'continue' was needed after start up.

The problem was that the 'emptyness' of m_cookieForToken was used as an
indication that there was no response packet still in the air. However,
this hash was not reset after a debugging session was aborted using S-F5,
so it could contain items from a previous run, effectively preventing
automatic triggering of the necessary 'continue'.