this changes mp_image_new_ref() to handle allocation failure itself
instead of doing it at its many call-sites (some of which never checked
for failure at all).
also remove MP_HANDLE_OOM() from the call sites since this is not
necessary anymore.
not all the call-sites have been touched, since some of the caller might
be relying on `mp_image_new_ref(NULL)` returning NULL.
Fixes: https://github.com/mpv-player/mpv/issues/11840
d70b859084