[Bug] should close ExtendableIterator when cassandra exception

[javeme]

Bug Type (问题类型)

logic (逻辑设计问题)

Before submit

• 我已经确认现有的 Issues 与 FAQ 中没有相同 / 重复问题

Environment (环境信息)

• Server Version: v0.11.x
• Backend: RocksDB x nodes, HDD or SSD
• OS: xx CPUs, xx G RAM, Centos 7.x
• Data Size: xx vertices, xx edges

Expected & Actual behavior (期望与实际表现)

ExtendableIterator<R> rs should be closed when an exception is encountered:
https://github.com/apache/incubator-hugegraph/blob/b699c5cd621ac91e53c08320c17902f401d3a391/hugegraph-cassandra/src/main/java/com/baidu/hugegraph/backend/store/cassandra/CassandraTable.java#L156

Vertex/Edge example (问题点 / 边数据举例)

No response

Schema [VertexLabel, EdgeLabel, IndexLabel] (元数据结构)

No response