stream-clone: bail-out earlier if destination repo is not empty...
stream-clone: bail-out earlier if destination repo is not empty
The `canperformstreamclone` function is bit messy. However it seems clearer to
me to process the very generic condition about "can we consider a stream-clone
at all", before checking if a stream-clone is requested and if a compatible
protocol can be negotiated with the server.
So I am doing some gratuitous movement so reorder conditional.
