handle nil case for vprovs in getter

x/colinearcore/memdb/biddb.go

@@ -226,6 +226,9 @@ func (b *auctionDB) GetVerifiedProviders(auctionId string) ([]string, error) {
 		return err
 	})
 	if err != nil {
+		if errors.Is(err, badger.ErrKeyNotFound) {
+			return []string{}, nil
+		}
 		return nil, err
 	}
 	if providers == nil {