zfs: recv: fix deadlock if streamCopier returns io.EOF

Close the write end of the pipe
* before we start waiting on the error channels
* and after everything from streamCopier has been written to the pipe

zfs/zfs.go

@@ -814,6 +814,7 @@ func ZFSRecv(ctx context.Context, fs string, streamCopier StreamCopier, opts Rec
 	copierErrChan := make(chan StreamCopierError)
 	go func() {
 		copierErrChan <- streamCopier.WriteStreamTo(stdinWriter)
+		stdinWriter.Close()
 	}()
 	waitErrChan := make(chan *ZFSError)
 	go func() {