Changed function to return -1 through SDL_Error() instead of plain -1.

src/render/SDL_render.c

@@ -348,8 +348,7 @@ SDL_GetRendererOutputSize(SDL_Renderer * renderer, int *w, int *h)
         return 0;
     } else {
         /* This should never happen */
-        SDL_SetError("Renderer doesn't support querying output size");
-        return -1;
+        return SDL_SetError("Renderer doesn't support querying output size");
     }
 }