Is it a good idea to guarantee a value of 0? Does it lead to a good practice?

As one of the commenters pointed out, there was at least one case when that wasn't true (which could cause a lot of current solutions, ignoring count, to overflow).

And if there is a reason behind it, then why bother with ARRAY_SIZE macro and passing count at all?
(Is that, perhaps, the way we bait for 'clever' sollutions here?)

Now I may be wrong here, but since when does malloc initialize contents of memory? AFAIK it could, but doesn't have to, and malloc(0) is a very specific case (implementation dependent) - it may either return NULL or a non-NULL pointer.
https://softwareengineering.stackexchange.com/questions/411166/why-would-you-ever-use-malloc0

I do believe that "already being a NULL was lucky" applies to your code as well - IMO both cases passed the test thanks to linux kernel.
https://stackoverflow.com/questions/45323930/is-malloc-initializing-allocated-array-to-zero

AFAIK the correct option should use calloc.

(Also your code could use some whitespaces after comas and semicolons or around operators . Readability is quite poor.)