No host client validation in `SV_HandleClientMessage` handler

[Xelson]

NextClientServerApi/src/main.cpp

Line 70 in ec05e53

void SV_HandleClientMessage(IRehldsHook_HandleNetCommand* hookchain, IGameClient* apiClient, int8 opcode)

There is a chance that host_client will be nullptr for e.g after other modules kick the player, before the chain reaches the module. Should be properly validated