(z) expansion flag do not always return an array

[Vincent Bernat <bernat@luffy.cx>]

Hey!

The (z) expansion flag is documented to return an array, but this is not
the case if we have only one word:

 16:24 ❱ print -l ${${(z)${:-word1}}[1]}
w
 16:24 ❱ print -l ${${(z)${:-word1 word2}}[1]}
word1

This can be worked around with A:

 16:29 ❱ print -l ${${(Az)${:-word1}}[1]}
word1
 16:29 ❱ print -l ${${(Az)${:-word1 word2}}[1]}
word1

But older versions of Zsh does not have that. Is there another way? Is
there an easy way to know if something is an array or a string? I am
using subscripting for that but maybe there are better ways.

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