## What changes were proposed in this pull request?
In `KafkaOffsetReader`, when error occurs, we abort the existing consumer and create a new consumer. In our current implementation, the first consumer and the second consumer would be in the same group (which leads to SPARK-19559), **_violating our intention of the two consumers not being in the same group._**
The cause is that, in our current implementation, the first consumer is created before `groupId` and `nextId` are initialized in the constructor. Then even if `groupId` and `nextId` are increased during the creation of that first consumer, `groupId` and `nextId` would still be initialized to default values in the constructor for the second consumer.
We should make sure that `groupId` and `nextId` are initialized before any consumer is created.
## How was this patch tested?
Ran 100 times of `KafkaSourceSuite`; all passed
Author: Liwei Lin <lwlin7@gmail.com>
Closes#16902 from lw-lin/SPARK-19564-.
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