Core/Logging: Force synchronous logging after io_service shutdown - fixes logging on worldserver shutdown

(cherry picked from commit a0b2be6c1d)

src/server/worldserver/Main.cpp

@@ -243,6 +243,8 @@ extern int main(int argc, char** argv)
     // Shutdown starts here
     ShutdownThreadPool(threadPool);
 
+    sLog->SetSynchronous();
+
     sScriptMgr->OnShutdown();
 
     sWorld->KickAll();                                       // save and kick all players