修复缓冲区消息多出一份的情况

[GXKe]

---

name: Pull request
about: Propose changes to the code
title: '修复消息多出一份的情况'
labels: ''
assignees: ''

version:v2.2.5

问题场景：

1. conn首次OnTraffic响应，未消费buf数据
2. 框架会复制保存buf到inboundBuffer _, _ = c.inboundBuffer.Write(c.buffer)
3. 异步协程wake唤醒conn
4. 此时conn.Peek出来的buf数据是两份 (c.inboundBuffer + c.buffer)

tcp read这里修复后已经用起来了
readUDP方法应该也需要修复测试一下

[panjf2000]

谢谢找到这个问题并发起 PR，我想针对这个 case 加一个测试在 gnet_test.go，请你有时间的时候在这个 PR 里加一下，谢谢！

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (edffef8) 76.46% compared to head (6966aa9) 76.46%.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #445   +/-   ##
=======================================
  Coverage   76.46%   76.46%           
=======================================
  Files          15       15           
  Lines        1500     1500           
=======================================
  Hits         1147     1147           
  Misses        271      271           
  Partials       82       82           

Flag	Coverage Δ
unittests	76.46% <100.00%> (ø)

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

Impacted Files	Coverage Δ
eventloop.go	71.90% <100.00%> (ø)

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