Prevents execution of the timer

[pi-pi-miao]

因为select随机执行，这里加入判断，防止多次执行定时器内容

[pi-pi-miao]

add case

[codecov]

Codecov Report

Merging #7 into master will increase coverage by 0.57%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master       #7      +/-   ##
==========================================
+ Coverage   90.84%   91.42%   +0.57%     
==========================================
  Files           3        3              
  Lines         404      408       +4     
==========================================
+ Hits          367      373       +6     
+ Misses         23       21       -2     
  Partials       14       14              

Impacted Files	Coverage Δ
watcher.go	93.87% <100.00%> (+0.77%)	⬆️

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