fix SetHostSocket when add stream failed

[lo-tk]

What problem does this PR solve?

Issue Number: introduced by PR #2938 .

Problem Summary:

Stream::SetHostSocket performs host-socket binding inside std::call_once, which makes the first execution result effectively global for all later callers. If AddStream(id()) fails during that first attempt, the lambda returns without setting _host_socket, but the once_flag is still consumed. After that, subsequent callers cannot retry the binding logic and may only observe the post-state through the function return value. This creates a broken state where the stream is not actually attached to any host socket, while later code paths still assume the binding has succeeded, eventually triggering _host_socket == NULL checks or null-dereference style crashes.

Changed:

return _host_socket != NULL ? 0 : -1;

Side effects:

• Performance effects:

• Breaking backward compatibility:

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Check List:

• Please make sure your changes are compilable.
• When providing us with a new feature, it is best to add related tests.
• Please follow Contributor Covenant Code of Conduct.

[Copilot]

Pull request overview

This PR adjusts brpc::Stream::SetHostSocket() (in src/brpc/stream.cpp) so it no longer reports success unconditionally after the std::call_once block, and instead returns failure when _host_socket was not actually bound—addressing a broken state that can occur when AddStream(id()) fails during the first (and only) call_once attempt.

Changes:

• Change Stream::SetHostSocket() to return 0 only when _host_socket is non-null, otherwise -1.

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[chenBright]

LGTM