Added a new unused key code from Android 4.4 (API 19).

src/video/android/SDL_androidkeyboard.c

@@ -262,6 +262,7 @@ static SDL_Scancode Android_Keycodes[] = {
     SDL_SCANCODE_UNKNOWN, /* AKEYCODE_ASSIST */
     SDL_SCANCODE_BRIGHTNESSDOWN, /* AKEYCODE_BRIGHTNESS_DOWN */
     SDL_SCANCODE_BRIGHTNESSUP, /* AKEYCODE_BRIGHTNESS_UP */
+    SDL_SCANCODE_UNKNOWN, /* AKEYCODE_MEDIA_AUDIO_TRACK */
 };
 
 static SDL_Scancode