Define WINVER in SDL_windowsjoystick.c if not defined. Related to #1629.

Source/ThirdParty/SDL/src/joystick/windows/SDL_windowsjoystick.c

@@ -18,6 +18,9 @@
      misrepresented as being the original software.
   3. This notice may not be removed or altered from any source distribution.
 */
+
+// Modified by Lasse Oorni for Urho3D
+
 #include "../../SDL_internal.h"
 
 #if SDL_JOYSTICK_DINPUT || SDL_JOYSTICK_XINPUT
@@ -45,6 +48,10 @@
 #if !SDL_EVENTS_DISABLED
 #include "../../events/SDL_events_c.h"
 #endif
+// Urho3D: set WINVER if not defined
+#ifndef WINVER
+#define WINVER 0x0500
+#endif
 #include "../../core/windows/SDL_windows.h"
 #if !defined(__WINRT__)
 #include <dbt.h>