fix the unstable socket connection error

[ababycat]

If notify_one() of the condition variable has been called before the function wait(), wait() blocks the connection until the next connection is established.

So you get an socket connect Error. #102 etc. It will occur more frequently on the iOS platform.

solution: Use FScopedEvent of UE to synchronize the finished status.

reference:

https://en.cppreference.com/w/cpp/thread/condition_variable/notify_one https://docs.unrealengine.com/4.26/en-US/API/Runtime/Core/Misc/FScopedEvent/

[tencent-adm]

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