stream-clone: bail-out earlier if pull is partial 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.

edition = "2018"
max_width = 79
wrap_comments = true
error_on_line_overflow = true