refactor: use let else to simplify huge if let block

[xxchan]

What's changed and what's your intention?

as title

Checklist

• I have written necessary docs and comments
• I have added necessary unit tests and integration tests

Refer to a related PR or issue link (optional)

[codecov]

Codecov Report

Merging #2162 (ad958fc) into main (918e661) will increase coverage by 0.00%.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##             main    #2162   +/-   ##
=======================================
  Coverage   70.51%   70.51%           
=======================================
  Files         645      645           
  Lines       81794    81782   -12     
=======================================
- Hits        57677    57669    -8     
+ Misses      24117    24113    -4     

Flag	Coverage Δ
rust	70.51% <0.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/meta/src/lib.rs	2.08% <ø> (ø)
...c/meta/src/stream/fragmenter/graph/stream_graph.rs	63.81% <0.00%> (+0.15%)	⬆️
src/meta/src/stream/stream_manager.rs	63.53% <0.00%> (-0.10%)	⬇️
src/connector/src/filesystem/file_common.rs	80.44% <0.00%> (-0.45%)	⬇️
src/frontend/src/optimizer/mod.rs	94.35% <0.00%> (-0.28%)	⬇️
.../src/executor/managed_state/aggregation/extreme.rs	90.02% <0.00%> (-0.27%)	⬇️
src/common/src/config.rs	79.16% <0.00%> (ø)
src/common/src/types/chrono_wrapper.rs	86.48% <0.00%> (ø)
... and 5 more

📣 Codecov can now indicate which changes are the most critical in Pull Requests. Learn more