Zero-Level Characters, Part 2: Magic-Users
As is all-too-normal these days, two Web searches on the identical keywords yielded different results. My search for “zero-level magic-users” before I posted Part 1 did not surface their mention in AD&D’s Unearthed Arcana rulebook. Here it is:

I do not remember this passage at all. I only remember zero-level options for the Cavalier class; also in Unearthed Arcana, but it was included in the original Dragon Magazine #72 article on the class.
It is very close to what I was thinking.