bug(channel): Do not close closed channel

[rustatian]

closes #2

[codecov]

Codecov Report

Merging #3 (52981c3) into master (41d3e70) will increase coverage by 9.80%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master       #3      +/-   ##
==========================================
+ Coverage   81.86%   91.66%   +9.80%     
==========================================
  Files           6        4       -2     
  Lines         193       96      -97     
==========================================
- Hits          158       88      -70     
+ Misses         22        5      -17     
+ Partials       13        3      -10     

Impacted Files	Coverage Δ
conn_context.go	100.00% <ø> (+12.50%)	⬆️
conn_pool.go	93.61% <ø> (-0.27%)	⬇️
service.go	100.00% <ø> (+26.31%)	⬆️
access_validator.go	80.76% <100.00%> (ø)
rpc.go
config.go

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