[#83] Don't create extra delete marker

We shouldn't create delete marker if:
1. object doesn't exist at all
2. last version is already a delete marker

Signed-off-by: Denis Kirillov <d.kirillov@yadro.com>

api/handler/handlers_test.go

@@ -33,6 +33,7 @@ type handlerContext struct {
 	t       *testing.T
 	h       *handler
 	tp      *layer.TestFrostFS
+	tree    *tree.Tree
 	context context.Context
 }
 
@@ -85,11 +86,13 @@ func prepareHandlerContext(t *testing.T) *handlerContext {
 	var owner user.ID
 	user.IDFromKey(&owner, key.PrivateKey.PublicKey)
 
+	treeMock := NewTreeServiceMock(t)
+
 	layerCfg := &layer.Config{
 		Caches:      layer.DefaultCachesConfigs(zap.NewExample()),
 		AnonKey:     layer.AnonymousKey{Key: key},
 		Resolver:    testResolver,
-		TreeService: NewTreeServiceMock(t),
+		TreeService: treeMock,
 	}
 
 	var pp netmap.PlacementPolicy
@@ -110,6 +113,7 @@ func prepareHandlerContext(t *testing.T) *handlerContext {
 		t:       t,
 		h:       h,
 		tp:      tp,
+		tree:    treeMock,
 		context: context.WithValue(context.Background(), api.BoxData, newTestAccessBox(t, key)),
 	}
 }