Passing write or readLength = 0 as an argument to emAfReadOrWriteAttribute is unsafe

[vivien-apple]

Passing a 0 readLength here is just asking for trouble in memory safety terms for both reads and writes. Please make sure a followup is filed to stop doing that, marked as a critical security problem. Or fix it before landing, I guess....

Originally posted by @bzbarsky-apple in #5020 (comment)

[tcarmelveilleux]

A bit more context since the original PR conversation link does not expand:

[bzbarsky-apple]

Note that the code in question (the caller of emAfReadOrWriteAttribute) is gone now. The API itself still has issues, but this callsite is not one of them.