web_service: follow-up fix to #4842 ...

* The web_service http request is now fixed on Windows (R) platform.
* The issue is due to a complicated race-condition in `httplib`, a detailed
  explanation is available at https://github.com/yhirose/cpp-httplib/pull/701
* A pending Pull Request on `httplib` has been applied to remedy the
  said race-condition.
* The socket availability check is removed due to a behavioral chice of
  `httplib` that a socket will not be created before any actual request
  is sent.