Better optional diag in t/sqlmaker/dbihacks_internals.t
One more fail-case missed in 135ac69dd

Now the test attached to RT#98161 actually passes... le sigh

At this point I am very wary of the entire codepath: yes, it is clearly the
right thing to do, and the logic is sound, but odd edge cases keep popping
up like this... OTOH there is no way to properly do equality inferrence
without this entire dance, in other words: rock&hardplace. Hopefully the
test suites will shake this out, apologoies to all affected :(
Add one more spot of unroll