Restore removed <algorithm> includes.

Turns out these were needed after all. For some reason, on Windows and
Mac, <algorithm> gets auto-included by something else so I don't notice
when it's missing, and MSVC's include dependency tracker doesn't see it
either.

Core/Screenshot.cpp

@@ -17,6 +17,8 @@
 
 #include "ppsspp_config.h"
 
+#include <algorithm>
+
 #include <png.h>
 #include "ext/jpge/jpge.h"