[Java] Null pointer closing unused JDBC Consumers

It’s legal to create a consumer that you never use, and then on close() vector will be null.

**Reporter**: [Larry White](https://issues.apache.org/jira/browse/ARROW-18179) / @lwhite1

_{**Note**: *This issue was originally created as [ARROW-18179](https://issues.apache.org/jira/browse/ARROW-18179). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

未指定源文件或测试。首先复现未使用的 JDBC Consumer 场景，并跟踪其 close() 路径；完成的标准是，关闭从未使用过的 consumer 不再引发空指针错误，并且为该情况提供回归覆盖。

由索引模型根据 Issue 内容生成。