FACE_FROM_ID vs FACE_OPT_FROM_ID

[Eli Zaretskii]

Paul, can you explain why we need two macros where we had only one?
Two macros with similar effect and unclear rules for when to use each
one doesn't sound like a good idea to me.  I've read the commit log
message, which attempts to explain the preference, but I don't think I
understand the criterion -- any face ID can cause FACE_FROM_ID to
produce NULL, if called in some inopportune moment.  I also looked at
the places where you used each macro, and I cannot understand why you
decided to use this or that, maybe I'm missing something.

What was the GCC 6.1 complaint that led you to this change?

Same questions for IMAGE_FROM_ID.