Fixed freeing the Windows blank cursor

src/video/windows/SDL_windowsmouse.c

@@ -372,7 +372,8 @@ WIN_QuitMouse(_THIS)
     }
 
     if (SDL_blank_cursor) {
-        SDL_FreeCursor(SDL_blank_cursor);
+        WIN_FreeCursor(SDL_blank_cursor);
+        SDL_blank_cursor = NULL;
     }
 }