fix: fix the bug which causes null pointer panic in loopCloseConn

[hihaha]

name: Pull request
about: Propose changes to the code
title: ''
labels: ''
assignees: ''

1. Are you opening this pull request for bug-fixs, optimizations or new feature?

2. Please describe how these code changes achieve your intention.

3. Please link to the relevant issues (if any).

4. Which documentation changes (if any) need to be made/updated because of this PR?

4. Checklist

• I have squashed all insignificant commits.
• I have commented my code for explaining package types, values, functions, and non-obvious lines.
• I have written unit tests and verified that all tests passes (if needed).
• I have documented feature info on the README (only when this PR is adding a new feature).
• (optional) I am willing to help maintain this change if there are issues with it later.

[codecov]

Codecov Report

Merging #111 into master will increase coverage by 0.21%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #111      +/-   ##
==========================================
+ Coverage   86.28%   86.50%   +0.21%     
==========================================
  Files          18       18              
  Lines        1400     1400              
==========================================
+ Hits         1208     1211       +3     
+ Misses        162      160       -2     
+ Partials       30       29       -1     

Impacted Files	Coverage Δ
eventloop_unix.go	76.82% <0.00%> (+1.82%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 38c6a25...5acbe41. Read the comment docs.

[panjf2000]

LGTM