fix(hash agg): don't emit data in HashAgg when stream is paused

[stdrc]

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What's changed and what's your intention?

Fix #19117.

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[stdrc]

• fix(hash agg): don't emit data in HashAgg when stream is paused #19168 👈
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[st1page]

Although the modification is simple, we may still need to test to ensure that it does not result in data loss.

🤔 But it seems hard to test in e2e test.

[fuyufjh]

I think we need to find out the sources of these watermark events. Because, technically, if there is not incomming events, the watermark won't be updated.

[stdrc]

I just realized that StreamSort can produce chunks when receiving watermark message. Now I agree that we shouldn't have watermark messages on the stream when the stream is paused.

[stdrc]

Superseded by #19199.