fix: redundant loop and nil check filterer

pkg/storage/stores/shipper/indexshipper/tsdb/single_file_index.go

@@ -293,8 +293,10 @@ func (i *TSDBIndex) Stats(ctx context.Context, _ string, from, through model.Tim
 		by := make(map[string]struct{})
 		if i.chunkFilter != nil {
 			filterer = i.chunkFilter.ForRequest(ctx)
-			for _, k := range i.chunkFilter.ForRequest(ctx).RequiredLabelNames() {
-				by[k] = struct{}{}
+			if filterer != nil {
+				for _, k := range filterer.RequiredLabelNames() {
+					by[k] = struct{}{}
+				}
 			}
 		}
 		for p.Next() {
@@ -368,9 +370,6 @@ func (i *TSDBIndex) Volume(
 		for k := range labelsToMatch {
 			by[k] = struct{}{}
 		}
-		for _, k := range targetLabels {
-			by[k] = struct{}{}
-		}
 
 		// If we are aggregating by series, we need to include all labels in the series required for filtering chunks.
 		if i.chunkFilter != nil {