overlay: fix mouse events queued up while overlay is hidden (#683)

## Link to GitHub Issue or related Pull Request, if one exists
continuation of #677

## Description of change
When overlay was hidden, when mouse buttons were clicked, they were
queued up and replayed when overlay became visible again.

This is due to improper usage of `GetAsyncKeyState`, per documentation.

## Testing

src/spice2x/launcher/superexit.cpp

@@ -67,7 +67,9 @@ namespace superexit {
                     }
                 }
 
-                bool async_key_exit = GetAsyncKeyState(VK_MENU) && GetAsyncKeyState(VK_F4);
+                bool async_key_exit =
+                    (GetAsyncKeyState(VK_MENU) & 0x8000) != 0 &&
+                    (GetAsyncKeyState(VK_F4) & 0x8000) != 0;
 
                 bool overlay_exit = false;
                 auto buttons = games::get_buttons_overlay(eamuse_get_game());