node/metabase: Don't create parent index from the 1st child on migration

Should have been done in bd36f5b.
First child in object split V2 scheme contains incomplete parent header.
Previously, following error could occur during v3->v4 metabase migration:
```
put metadata for parent of object <OID>: missing payload checksum
```

This makes corresponding migration func to skip parent header from the
1st child as `Put` does.

Refs #3058.

Signed-off-by: Leonard Lyubich <[email protected]>

CHANGELOG.md

@@ -9,6 +9,7 @@ Changelog for NeoFS Node
 - Zero range denial by `neofs-cli object range|hash` commands (#3182)
 - Not all the components needed for write-cache migration were initialized (#3186)
 - Homomorphic hash indexes with empty values in meta bucket (#3187)
+- Failure of 1st split-chain child processing during metabase migration (#3187)
 
 ### Changed
 

pkg/local_object_storage/metabase/version.go

@@ -141,7 +141,7 @@ func migrateFrom3Version(_ *DB, tx *bbolt.Tx) error {
 			if err := putMetadataForObject(tx, hdr, hasParent, true); err != nil {
 				return fmt.Errorf("put metadata for object %s: %w", id, err)
 			}
-			if hasParent {
+			if hasParent && !par.GetID().IsZero() { // skip the first object without useful info similar to DB.put
 				if err := putMetadataForObject(tx, *par, false, false); err != nil {
 					return fmt.Errorf("put metadata for parent of object %s: %w", id, err)
 				}