fix: rootmulti's Restore don't return the next unknown item as expected (#11286)

## Description
Solution:
- return the next unknown item and add a unit test to ensure that.





---

### Author Checklist

*All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.*

I have...

- [ ] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] added `!` to the type prefix if API or client breaking change
- [ ] targeted the correct branch (see [PR Targeting](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#pr-targeting))
- [ ] provided a link to the relevant issue or specification
- [ ] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/master/docs/building-modules)
- [ ] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#testing)
- [ ] added a changelog entry to `CHANGELOG.md`
- [ ] included comments for [documenting Go code](https://blog.golang.org/godoc)
- [ ] updated the relevant documentation or specification
- [ ] reviewed "Files changed" and left comments if necessary
- [ ] confirmed all CI checks have passed

### Reviewers Checklist

*All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.*

I have...

- [ ] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] confirmed `!` in the type prefix if API or client breaking change
- [ ] confirmed all author checklist items have been addressed 
- [ ] reviewed state machine logic
- [ ] reviewed API design and naming
- [ ] reviewed documentation is accurate
- [ ] reviewed tests and test coverage
- [ ] manually tested (if applicable)

store/rootmulti/snapshot_test.go

@@ -182,6 +182,14 @@ func TestMultistoreSnapshotRestore(t *testing.T) {
 	target := newMultiStoreWithMixedMounts(dbm.NewMemDB())
 	version := uint64(source.LastCommitID().Version)
 	require.EqualValues(t, 3, version)
+	dummyExtensionItem := snapshottypes.SnapshotItem{
+		Item: &snapshottypes.SnapshotItem_Extension{
+			Extension: &snapshottypes.SnapshotExtensionMeta{
+				Name:   "test",
+				Format: 1,
+			},
+		},
+	}
 
 	chunks := make(chan io.ReadCloser, 100)
 	go func() {
@@ -190,12 +198,16 @@ func TestMultistoreSnapshotRestore(t *testing.T) {
 		defer streamWriter.Close()
 		err := source.Snapshot(version, streamWriter)
 		require.NoError(t, err)
+		// write an extension metadata
+		err = streamWriter.WriteMsg(&dummyExtensionItem)
+		require.NoError(t, err)
 	}()
 
 	streamReader, err := snapshots.NewStreamReader(chunks)
 	require.NoError(t, err)
-	_, err = target.Restore(version, snapshottypes.CurrentFormat, streamReader)
+	nextItem, err := target.Restore(version, snapshottypes.CurrentFormat, streamReader)
 	require.NoError(t, err)
+	require.Equal(t, *dummyExtensionItem.GetExtension(), *nextItem.GetExtension())
 
 	assert.Equal(t, source.LastCommitID(), target.LastCommitID())
 	for key, sourceStore := range source.GetStores() {

store/rootmulti/store.go

@@ -755,9 +755,11 @@ func (rs *Store) Restore(
 	// a SnapshotStoreItem, telling us which store to import into. The following items will contain
 	// SnapshotNodeItem (i.e. ExportNode) until we reach the next SnapshotStoreItem or EOF.
 	var importer *iavltree.Importer
+	var snapshotItem snapshottypes.SnapshotItem
+loop:
 	for {
-		snapshotItem := &snapshottypes.SnapshotItem{}
-		err := protoReader.ReadMsg(snapshotItem)
+		snapshotItem = snapshottypes.SnapshotItem{}
+		err := protoReader.ReadMsg(&snapshotItem)
 		if err == io.EOF {
 			break
 		} else if err != nil {
@@ -811,8 +813,7 @@ func (rs *Store) Restore(
 			}
 
 		default:
-			// pass back the unrecognized item.
-			return *snapshotItem, nil
+			break loop
 		}
 	}
 
@@ -825,7 +826,7 @@ func (rs *Store) Restore(
 	}
 
 	flushMetadata(rs.db, int64(height), rs.buildCommitInfo(int64(height)), []int64{})
-	return snapshottypes.SnapshotItem{}, rs.LoadLatestVersion()
+	return snapshotItem, rs.LoadLatestVersion()
 }
 
 func (rs *Store) loadCommitStoreFromParams(key types.StoreKey, id types.CommitID, params storeParams) (types.CommitKVStore, error) {