When we are asked to unthrottle an SSH connection (by the front end

calling back->unthrottle), we should immediately call
ssh_process_queued_incoming_data to handle the SSH packets that have
been saved for later functioning while we were throttled. Otherwise,
they'll sit there unhandled until the next call to ssh_gotdata, which
might not be for ages if the server thinks it's waiting for us.

git-svn-id: svn://svn.tartarus.org/sgt/putty@9523 cda61777-01e9-0310-a592-d414129be87e