Fixed compiling with older Windows SDKs

src/core/windows/SDL_windows.h

@@ -41,7 +41,7 @@
 #elif defined(HAVE_SHELLSCALINGAPI_H)
 #define _WIN32_WINNT 0x603 /* For DPI support */
 #else
-#define _WIN32_WINNT 0x501 /* Need 0x410 for AlphaBlend() and 0x500 for EnumDisplayDevices(), 0x501 for raw input */
+#define _WIN32_WINNT 0x502 /* Need 0x410 for AlphaBlend() and 0x500 for EnumDisplayDevices(), 0x501 for raw input, 0x502 for RegGetValue() */
 #endif
 #define WINVER _WIN32_WINNT