[stable33] fix: only use unencrypted_size if set to a value - #64964

Resolves e2ee which cannot store unencrypted size displaying size `0 B`
because the Cache entry is initialized always to `unencrypted_size = 0`
in `cacheEntryFromData`.

Signed-off-by: Ferdinand Thiessen <opensource@fthiessen.de>

…d files

Preferring `unencrypted_size` only when it is greater than zero also drops
the plaintext size of a server side encrypted file whose content is empty,
where the cache holds `size` of one encryption header and `unencrypted_size`
of 0.

Only files carry the server side encryption mark, so an `encrypted` folder
got the flag from end-to-end encryption, which does not maintain
`unencrypted_size`. Decide by node type instead and route the three
diverging conditions through one predicate.

Assisted-by: ClaudeCode:claude-opus-5
Signed-off-by: Ferdinand Thiessen <opensource@fthiessen.de>