fix: repair each block length even without an else

[paoloricciuti]

Svelte 5 rewrite

Fixes #12095

I don't know if it's the correct approach but tests are all greens and it fixes the problem. As i've explained in the comments the error was happening because if the length on the server was 0 hydration was only set to false if an {:else} branch was specified by the user.

Initially i thought of always add the HIDRATION_END_ELSE marker if the array length was 0 on the server (even if the fallback was not provided by the user) but this would've add an if for every each. So i tried to infer if the length was 0 in another way and i come up with the idea of checking the length of hydrate_nodes but to be fair i don't know if this is correct so i would appreciate some input.

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[Rich-Harris]

Thanks — am trying to avoid adding any more dependency on hydrate_nodes as I'd like to get rid of it at some point. Checking hydrate_start === undefined is easier and serves the same purpose

[paoloricciuti]

Thanks — am trying to avoid adding any more dependency on hydrate_nodes as I'd like to get rid of it at some point. Checking hydrate_start === undefined is easier and serves the same purpose

Gotcha...i'm trying to get around to better understand hydration but i think this is the first time i really interacted with hydration code so i only have a general understanding of it.