### What changes were proposed in this pull request?
Fix the refactor bug of CELEBORN-614 (https://github.com/apache/incubator-celeborn/pull/1517).
### Why are the changes needed?
This is a bug fix, the condition `writer.getException != null` was inverted accidentally during CELEBORN-614 (https://github.com/apache/incubator-celeborn/pull/1517), which causes the trim became no-op.
### Does this PR introduce _any_ user-facing change?
No. The bug was caused by an unreleased commit.
### How was this patch tested?
Set Worker off-heap memory to 2G, and run 1T tera sort.
Before: the trim does not trigger disk buffer flush, causing the worker can not to recover from the pause pushdata state, then Job failed.
After: the trim correctly triggers disk buffer flush, releases the worker memory, and the Job succeeded.
<img width="1653" alt="image" src="https://github.com/apache/incubator-celeborn/assets/26535726/9ef62c78-e6a9-497f-9dac-d3f712e830cc">
Closes#1689 from pan3793/CELEBORN-614-followup.
Authored-by: Cheng Pan <chengpan@apache.org>
Signed-off-by: mingji <fengmingxiao.fmx@alibaba-inc.com>
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