[tz] Bug in 2022f version of zic.c

[Clive D.W. Feather]

Paul Eggert via tz said:
> It's unfortunate that the C standard allows malloc to return NULL on 
> success, as this complicates error checking. Of course zic.c should be 
> portable even to platforms that exploit this glitch in C.

We're back to the "there are no zero-sized objects in C" point. Therefore
malloc(0) is an error by definition.

I remember us coming up with the compromise wording that allowed either
failure or success (but you can't access the returned memory), but I don't
recall the details of why.

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Clive D.W. Feather          | If you lie to the compiler,
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