Update \returns to the generic form

include/SDL3/SDL_misc.h

@@ -61,8 +61,8 @@ extern "C" {
  *
  * \param url A valid URL/URI to open. Use `file:///full/path/to/file` for
  *            local files, if supported.
- * \returns 0 on success, or -1 on error; call SDL_GetError() for more
- *          information.
+ * \returns 0 on success or a negative error code on failure; call
+ *          SDL_GetError() for more information.
  *
  * \since This function is available since SDL 3.0.0.
  */