Fix transitive includes in Screen.cpp

Screen.cpp wasn't explicitly including SDL.h, instead relying on
Screen.h to include it.

It was also relying on SDL.h to include stdio.h on Linux, which breaks
because SDL.h doesn't include stdio.h on Windows. So stdio.h is now
explicitly included as well.

stdlib.h is not used in this file.

desktop_version/src/Screen.cpp

@@ -1,6 +1,7 @@
 #include "Screen.h"
 
-#include <stdlib.h>
+#include <SDL.h>
+#include <stdio.h>
 
 #include "FileSystemUtils.h"
 #include "GraphicsUtil.h"