window_sdl2: prevent a compiler warning about num not initialized
window_sdl2: prevent a compiler warning about num not initialized

matham/kivy,kivy/kivy,akshayaurora/kivy,rnixx/kivy,inclement/kivy,akshayaurora/kivy,matham/kivy,inclement/kivy,matham/kivy,rnixx/kivy,kivy/kivy,rnixx/kivy,akshayaurora/kivy,kivy/kivy,inclement/kivy,matham/kivy