make sfRenderStates_default an extern const variable

include/CSFML/Graphics/RenderStates.h

@@ -50,4 +50,4 @@ typedef struct
 /// \brief Define the default values for a RenderState
 ///
 ////////////////////////////////////////////////////////////
-CSFML_GRAPHICS_API sfRenderStates sfRenderStates_default(void);
+CSFML_GRAPHICS_API const sfRenderStates sfRenderStates_default;

src/CSFML/Graphics/RenderStates.cpp

@@ -29,13 +29,9 @@
 
 
 ////////////////////////////////////////////////////////////
-sfRenderStates sfRenderStates_default()
-{
-    sfRenderStates states = {
-        sfBlendAlpha,
-        sfTransform_Identity,
-        nullptr,
-        nullptr,
-    };
-    return states;
-}
+const sfRenderStates sfRenderStates_default = {
+    sfBlendAlpha,
+    sfTransform_Identity,
+    nullptr,
+    nullptr,
+};