SteamSocketEventHandler missing nullptr check crashes server

FSteamSocketsSubsystem::SteamSocketEventHandler doesn't check for SocketInfo being nullptr, which can be exploited to crash a server.

https://github.com/EpicGames/UnrealEngine/blob/4.27/Engine/Plugins/Runtime/Steam/SteamSockets/Source/SteamSockets/Private/SteamSocketsSubsystem.cpp#L858

Here are some of the crash minidumps from this exploit.