Core/Misc: Fix for builds linked with libc++ instead of libstdc++

src/server/bnetserver/Server/Session.cpp

@@ -672,6 +672,7 @@ bool Battlenet::Session::Update()
     if (_queryFuture.valid() && _queryFuture.wait_for(std::chrono::seconds(0)) == std::future_status::ready)
     {
         auto callback = std::move(_queryCallback);
+        _queryCallback = nullptr;
         callback(_queryFuture.get());
     }
 

src/server/game/Server/WorldSocket.cpp

@@ -130,6 +130,7 @@ bool WorldSocket::Update()
         if (_queryFuture.valid() && _queryFuture.wait_for(std::chrono::seconds(0)) == std::future_status::ready)
         {
             auto callback = std::move(_queryCallback);
+            _queryCallback = nullptr;
             callback(_queryFuture.get());
         }
     }