[steam] Add SteamAPI_ISteamClient_BReleaseSteamPipe - #657

Than you, I'll look and test it soon!

It's only 5 lines - not the biggest PR :)

I'd already written it so hopefully saved you a few mins

Sorry for a delay with this, I have this PR on a list of TODOs for next week. Thanks for the patience :)

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I know, it's a short PR, but I do need to test whether it doesn't cause any regressions on the existing platforms, Linux, Windows, macOS.

If you want to help me speed it up, I will appreciate if you add a comment justifying the need for this to the source code , before the SteamAPI_ISteamClient_BReleaseSteamPipe. I recall you described it in one of the previous PRs, let's copy/adjust that description into a Pascal comment, so that it stays forever recorded. Like

  if Enabled then
  begin
    { Without doing SteamAPI_ISteamClient_BReleaseSteamPipe , an invalid behavior occurs when X. 
       Reproduce it by doing Y ...  }
    SteamAPI_ISteamClient_BReleaseSteamPipe(SteamClient, SteamPipeHandle);
    SteamAPI_Shutdown();
  end;

Thank you!
)