This reverts commit a9693064.

As mentioned in [LysLysKOM 20949405] (which probably hasn't been
exported correctly to the mailinglist yet):

The old code looks correct to me.

  * Restore s->s->len to the value it had when s->s was allocated
    (aka s->malloced).

  * Reallocate s->s with the new (now known) final length.

The question does however arise whether the code is correct on
realloc failure.