[#xx] metabase: Refactor selectNFromBucket

The function is riskly long. so adding just a few lines of code
might trigger the `funlen` linter. Kept the changes minimal:
- Moved the logic for filling object info into a separate function
- Preserved all existing side effects

Signed-off-by: Aleksey Savchuk <a.savchuk@yadro.com>

pkg/local_object_storage/metabase/list.go

@@ -243,34 +243,47 @@ func selectNFromBucket(bkt *bbolt.Bucket, // main bucket
 			continue
 		}
 
-		var isLinkingObj bool
-		var ecInfo *objectcore.ECInfo
-		if objType == objectSDK.TypeRegular {
-			var o objectSDK.Object
-			if err := o.Unmarshal(bytes.Clone(v)); err != nil {
-				return nil, nil, nil, err
-			}
-			isLinkingObj = isLinkObject(&o)
-			ecHeader := o.ECHeader()
-			if ecHeader != nil {
-				ecInfo = &objectcore.ECInfo{
-					ParentID: ecHeader.Parent(),
-					Index:    ecHeader.Index(),
-					Total:    ecHeader.Total(),
-				}
-			}
-		}
-
 		var a oid.Address
 		a.SetContainer(cnt)
 		a.SetObject(obj)
-		to = append(to, objectcore.Info{Address: a, Type: objType, IsLinkingObject: isLinkingObj, ECInfo: ecInfo})
+
+		info, err := prepareObjectInfo(objType, a, v)
+		if err != nil {
+			return nil, nil, nil, err
+		}
+
+		to = append(to, info)
 		count++
 	}
 
 	return to, offset, cursor, nil
 }
 
+func prepareObjectInfo(objType objectSDK.Type, addr oid.Address, obj []byte) (objectcore.Info, error) {
+	if objType != objectSDK.TypeRegular {
+		return objectcore.Info{Address: addr, Type: objType, IsLinkingObject: false, ECInfo: nil}, nil
+	}
+
+	var o objectSDK.Object
+	if err := o.Unmarshal(bytes.Clone(obj)); err != nil {
+		return objectcore.Info{}, err
+	}
+
+	info := objectcore.Info{
+		Address:         addr,
+		Type:            objType,
+		IsLinkingObject: isLinkObject(&o),
+	}
+	if ecHeader := o.ECHeader(); ecHeader != nil {
+		info.ECInfo = &objectcore.ECInfo{
+			ParentID: ecHeader.Parent(),
+			Index:    ecHeader.Index(),
+			Total:    ecHeader.Total(),
+		}
+	}
+	return info, nil
+}
+
 func parseContainerIDWithPrefix(containerID *cid.ID, name []byte) ([]byte, byte) {
 	if len(name) < bucketKeySize {
 		return nil, 0