* keep cached avatar&banner when refresh fails to get new values

when the remote explicitly tells us a user image is gone, we remove
our cached value, but if we fail to get the image, we keep whatever
value we already have

this should minimise the problem of avatars randomly disappearing

* autogen bits

* pnpm run build-misskey-js-with-types

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Co-authored-by: tamaina <tamaina@hotmail.co.jp>