## Link to GitHub Issue or related Pull Request, if one exists
#720
## Description of change
Pass `VK_F4` sys-key messages through to `DefWindowProc` before ImGui
ingestion, restoring the normal Alt+F4 -> `WM_CLOSE` ->
`launcher::shutdown()` path.
## Testing
- [x] Launch `spicecfg` (D3D9 default path) and press Alt+F4; window
closes and process exits
- [x] Launch `spicecfg` (software path) and press Alt+F4; window closes
and process exits
- [x] Close via title-bar X; still works
drmext
465d6c6c18