Fix rwops and some image stuff on SDL3

[ankith26]

• Fixes image saving return code handling.
• SDL_INIT_INTERFACE needs to be used on a SDL_IOStreamInterface interface.
• As a result of the above issue we were going into the error handling path where _pg_rw_close already does PyMem_Free(helper);, resulting in a double free.

With these changes all imageext tests pass and some failing image tests are also passing now.

[MightyJosip]

Can you do it like this #3515 (without adding new #if SDL_VERSION)

[ankith26]

I can do that but I don't see the need for doing it for functions that are used only once.