don't print a receive buffer warning for closed connections

[marten-seemann]

Fixes #3341.

[codecov]

Codecov Report

Merging #3346 (3831bdb) into master (ad1cb27) will decrease coverage by 0.01%.
The diff coverage is 60.00%.

@@            Coverage Diff             @@
##           master    #3346      +/-   ##
==========================================
- Coverage   85.51%   85.50%   -0.01%     
==========================================
  Files         135      135              
  Lines        9829     9830       +1     
==========================================
  Hits         8405     8405              
- Misses       1046     1047       +1     
  Partials      378      378              

Impacted Files	Coverage Δ
packet_handler_map.go	74.40% <60.00%> (+0.10%)	⬆️
internal/utils/rand.go	62.50% <0.00%> (-12.50%)	⬇️

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