client: reset encoders between uses

According to go/codec's docs, Reset(...) should be called on
Decoders/Encoders before reuse:

https://godoc.org/github.com/ugorji/go/codec

I could find no evidence that *not* calling Reset() caused bugs, but
might as well do what the docs say?

command/agent/fs_endpoint.go

@@ -361,6 +361,7 @@ func (s *HTTPServer) fsStreamImpl(resp http.ResponseWriter,
 			cancel()
 			return
 		}
+		encoder.Reset(httpPipe)
 
 		for {
 			select {
@@ -377,6 +378,7 @@ func (s *HTTPServer) fsStreamImpl(resp http.ResponseWriter,
 				cancel()
 				return
 			}
+			decoder.Reset(httpPipe)
 
 			if err := res.Error; err != nil {
 				if err.Code != nil {