Fixed bug 1882 - SDL_GetKeyboardState should return const.

Yuri K. Schlesner

The array returned by SDL_GetKeyboardState is also used internally by SDL to keep track of pressed/released keys and must not be modified, lest weird behaviour occurs. Because of this I believe it's return type should be changed to return a const pointer, which will provide a code indication of that fact.

src/events/SDL_keyboard.c

@@ -829,7 +829,7 @@ SDL_KeyboardQuit(void)
 {
 }
 
-Uint8 *
+const Uint8 *
 SDL_GetKeyboardState(int *numkeys)
 {
     SDL_Keyboard *keyboard = &SDL_keyboard;