Fix crash on closing game during background image upscaling

clientapp/EntryPoint.cpp

@@ -27,6 +27,7 @@
 #include "../client/windows/CMessage.h"
 #include "../client/windows/InfoWindows.h"
 
+#include "../lib/AsyncRunner.h"
 #include "../lib/CConsoleHandler.h"
 #include "../lib/CConfigHandler.h"
 #include "../lib/CThreadHelper.h"
@@ -417,6 +418,9 @@ int main(int argc, char * argv[])
 		vstd::clear_pointer(graphics);
 	}
 
+	// must be executed before reset - since unique_ptr resets pointer to null before calling destructor
+	ENGINE->async().wait();
+
 	ENGINE.reset();
 
 	vstd::clear_pointer(LIBRARY);