shade: fix uploads failing with EOF when completing multipart uploads

The multipart upload complete endpoint returns 200 with an empty body,
but rclone tried to decode that body as JSON, failed with EOF and
retried until the retries ran out, so every upload failed even though
the server had actually completed it.

Fixed by not attempting to decode the response body.

This was a regression introduced in

a4972de505 shade: retry server errors instead of failing the transfer

which started treating the JSON decode error as fatal where previously
it was accidentally ignored.

backend/shade/upload.go

@@ -17,7 +17,6 @@ import (
 	"github.com/rclone/rclone/backend/shade/api"
 	"github.com/rclone/rclone/fs"
 	"github.com/rclone/rclone/fs/chunksize"
-	"github.com/rclone/rclone/fs/fserrors"
 	"github.com/rclone/rclone/lib/multipart"
 	"github.com/rclone/rclone/lib/rest"
 )
@@ -255,30 +254,20 @@ func (s *shadeChunkWriter) Close(ctx context.Context) error {
 		return err
 	}
 
+	// The complete response has an empty body so don't attempt to decode it
 	completeOpts := rest.Opts{
-		Method:  "POST",
-		Path:    fmt.Sprintf("/%s/upload/multipart/complete?token=%s", s.f.drive, url.QueryEscape(s.initToken)),
-		RootURL: s.f.endpoint,
+		Method:     "POST",
+		Path:       fmt.Sprintf("/%s/upload/multipart/complete?token=%s", s.f.drive, url.QueryEscape(s.initToken)),
+		RootURL:    s.f.endpoint,
+		NoResponse: true,
 		ExtraHeaders: map[string]string{
 			"Authorization": "Bearer " + token,
 		},
 	}
 
-	var response http.Response
-
 	err = s.f.pacer.Call(func() (bool, error) {
-		res, err := s.f.srv.CallJSON(ctx, &completeOpts, completeBody, &response)
-
-		if err != nil {
-			return shouldRetry(ctx, res, err)
-		}
-
-		if res.StatusCode != http.StatusOK && res.StatusCode != http.StatusCreated {
-			body, _ := io.ReadAll(res.Body)
-			return fserrors.ShouldRetryHTTP(res, retryErrorCodes), fmt.Errorf("complete multipart failed with status %d: %s", res.StatusCode, string(body))
-		}
-
-		return false, nil
+		res, err := s.f.srv.CallJSON(ctx, &completeOpts, completeBody, nil)
+		return shouldRetry(ctx, res, err)
 	})
 
 	if err != nil {