[#659] fix(server): fix NPE of ShuffleDataFlushEvent's underStorage in some cases

[zuston]

What changes were proposed in this pull request?

fix NPE of ShuffleDataFlushEvent's underStorage in some cases

Why are the changes needed?

Fix: #659

Does this PR introduce any user-facing change?

No.

How was this patch tested?

Existing UTs

[codecov-commenter]

Codecov Report

Merging #660 (f760334) into master (18c738e) will increase coverage by 2.28%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #660      +/-   ##
============================================
+ Coverage     60.60%   62.89%   +2.28%     
- Complexity     1799     1801       +2     
============================================
  Files           216      202      -14     
  Lines         12458    10494    -1964     
  Branches       1052     1052              
============================================
- Hits           7550     6600     -950     
+ Misses         4500     3547     -953     
+ Partials        408      347      -61     

Impacted Files	Coverage Δ
...g/apache/uniffle/server/ShuffleDataFlushEvent.java	83.67% <100.00%> (ø)
...bernetes/operator/pkg/controller/controller/rss.go
...oy/kubernetes/operator/pkg/controller/util/util.go
...rnetes/operator/pkg/webhook/inspector/inspector.go
deploy/kubernetes/operator/pkg/utils/certs.go
...pkg/controller/sync/shuffleserver/shuffleserver.go
...y/kubernetes/operator/pkg/webhook/inspector/rss.go
...oy/kubernetes/operator/pkg/utils/shufflerserver.go
deploy/kubernetes/operator/pkg/utils/config.go
deploy/kubernetes/operator/pkg/utils/util.go
... and 6 more

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[jerqi]

LGTM, thanks @advancedxy @zuston ,merged to master & 0.7