Fix off-by-one error when updating old messages.
:: changed message
%_ +>.$
grams %+ welp
- (scag (dec (max u.old 1)) grams)
- [gam (slag u.old grams)]
+ (scag u.old grams)
+ [gam (slag +(u.old) grams)]
==
::
++ sa-change-remote ::< apply remote's delta
