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

[tokers]

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

• The sister PR: improve: checking ev->pending_eof before peeking data from tcp buffer meta-lua-nginx-module#69
• Relevant issue: worker process suffers CPU 100% usage stream-lua-nginx-module#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.