improve: checking ev->pending_eof before peeking data from tcp buffer

[tokers]

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I hereby granted the copyright of the changes in this pull request to the authors of this lua-nginx-module project.

• The sister PR: https://github.com/openresty/meta-lua-nginx-module/pull/69
• Relevant issue: https://github.com/openresty/stream-lua-nginx-module/issues/167

[doujiang24]

@tokers good job :) we need some test cases to for it :)

[tokers]

@doujiang24 Sure :). I will add test cases as soon as possible.