fix: worker_threads mode without ports

[sjfkai]

fix: worker_threads 模式下，指定 port 不指定 ports 时， port 不生效的问题

• 复现方式：

$ PORT=8080 egg-scripts start --title=egg-server-xxx --workers=1 --startMode worker_threads

• 实际结果：

监听7001端口

• 期望结果：

监听8080端口

Checklist

• npm test passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

Description of change

[fengmk2]

目前线程模式没法监听同一个端口。

[sjfkai]

目前线程模式没法监听同一个端口。

不是监听同一个端口的问题。而是没有传 ports 参数时，port参数也没有生效的问题。

这个改动是当没有指定 ports 却指定了 port 时， ports 默认为 [port]

[codecov]

Codecov Report

Base: 93.51% // Head: 93.53% // Increases project coverage by +0.01% 🎉

Coverage data is based on head (dffbf67) compared to base (5a656e4).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #103      +/-   ##
==========================================
+ Coverage   93.51%   93.53%   +0.01%     
==========================================
  Files          12       12              
  Lines         787      789       +2     
  Branches      119      119              
==========================================
+ Hits          736      738       +2     
  Misses         51       51              

Impacted Files	Coverage Δ
lib/utils/mode/impl/worker_threads/app.js	69.41% <100.00%> (+0.73%)	⬆️

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