bug#31446: 26.1; sql-interactive-mode buffer naming is broken

[Phil Sainty]

Hi Eli,

Apologies for lack of testing; I was away while the fix was
being discussed.

I'll need to test more thoroughly later, but I can tell you
that the current code isn't working, as the (zerop new-name)
condition produces code like (= 0 nil) or (= 0 '(4)) which
results in, e.g., (wrong-type-argument number-or-marker-p (4))