Android: prevent concurrency in Android_SetScreenResolution() when exiting
by checking Android_Window validity

- SDLThread: user application is exiting:
    SDL_VideoQuit() and clearing SDL_GetVideoDevice()

- ActivityThread is changing orientation/size
    surfaceChanged() > Android_SetScreenResolution() > SDL_GetVideoDevice()

- Separate function into Android_SetScreenResolution() and Android_SendResize(),
    formating, and mark Android_DeviceWidth/Heigh as static
4 files changed