bugfix: "path=/" will cause panic

[rinfx]

如果请求 path 为空，在处理请求头阶段将不会设置以下kv：ctx.SetContext("httpProtocol", string(protocol)) ，而处理响应头阶段会用到httpProtocol，此时类型转换失败，触发panic。将相关代码位置提前可以避免此情况发生。

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 38.14%. Comparing base (612c94d) to head (33bb027).
⚠️ Report is 945 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #809      +/-   ##
==========================================
- Coverage   38.17%   38.14%   -0.03%     
==========================================
  Files          61       61              
  Lines       10412    10412              
==========================================
- Hits         3975     3972       -3     
- Misses       6138     6140       +2     
- Partials      299      300       +1     

see 1 file with indirect coverage changes

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[johnlanni]

LGTM