[#268] client: Fix sequential PayloadPatch calls

* The flag 'firstPayloadPatch' keeps its state after first
  `PatchPayload` that make other calls incorrectly set patch
  ranges.

Signed-off-by: Airat Arifullin <a.arifullin@yadro.com>

client/object_patch.go

@@ -106,7 +106,6 @@ func (c *Client) ObjectPatchInit(ctx context.Context, prm PrmObjectPatch) (Objec
 	}
 	objectPatcher.client = c
 	objectPatcher.stream = stream
-	objectPatcher.firstPatchPayload = true
 
 	if prm.MaxChunkLength > 0 {
 		objectPatcher.maxChunkLen = prm.MaxChunkLength
@@ -154,8 +153,6 @@ type objectPatcher struct {
 	respV2 v2object.PatchResponse
 
 	maxChunkLen int
-
-	firstPatchPayload bool
 }
 
 func (x *objectPatcher) PatchAttributes(_ context.Context, newAttrs []object.Attribute, replace bool) bool {
@@ -171,7 +168,7 @@ func (x *objectPatcher) PatchPayload(_ context.Context, rng *object.Range, paylo
 
 	buf := make([]byte, x.maxChunkLen)
 
-	for {
+	for patchIter := 0; ; patchIter++ {
 		n, err := payloadReader.Read(buf)
 		if err != nil && err != io.EOF {
 			x.err = fmt.Errorf("read payload: %w", err)
@@ -182,8 +179,7 @@ func (x *objectPatcher) PatchPayload(_ context.Context, rng *object.Range, paylo
 		}
 
 		rngPart := object.NewRange()
-		if x.firstPatchPayload {
-			x.firstPatchPayload = false
+		if patchIter == 0 {
 			rngPart.SetOffset(offset)
 			rngPart.SetLength(rng.GetLength())
 		} else {

client/object_patch_test.go

@@ -170,12 +170,11 @@ func TestObjectPatcher(t *testing.T) {
 			pk, _ := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
 
 			patcher := objectPatcher{
-				client:            &Client{},
-				stream:            m,
-				addr:              oidtest.Address(),
-				key:               pk,
-				maxChunkLen:       test.maxChunkLen,
-				firstPatchPayload: true,
+				client:      &Client{},
+				stream:      m,
+				addr:        oidtest.Address(),
+				key:         pk,
+				maxChunkLen: test.maxChunkLen,
 			}
 
 			success := patcher.PatchAttributes(context.Background(), nil, false)