HOTFIX: Close unused ColumnFamilyHandle (#6893)

In RocksDBTimestampedStore#openRocksDB we try to open a db with two column families. If this succeeds but the first column family is empty (db.newIterator.seekToFirst.isValid() == false) we never actually close its ColumnFamilyHandle

Reviewers: Matthias J. Sax <matthias@confluent.io>, Guozhang Wang <wangguoz@gmail.com>

streams/src/main/java/org/apache/kafka/streams/state/internals/RocksDBTimestampedStore.java

@@ -81,6 +81,7 @@ public class RocksDBTimestampedStore extends RocksDBStore implements Timestamped
             } else {
                 log.info("Opening store {} in regular mode", name);
                 dbAccessor = new SingleColumnFamilyAccessor(columnFamilies.get(1));
+                noTimestampColumnFamily.close();
             }
             noTimestampsIter.close();
         } catch (final RocksDBException e) {