Add64 checked currentNum > max only after already mutating currentNum
and currentBytes, so a single call that overshoots max returned an
error but left the bar stuck: currentNum frozen above max, percent
stuck above 100%, and every later Add/Set call failing with the same
error forever, since the top-of-function currentNum < max guard could
never pass again.
Check the bound before mutating state instead, so an overshooting call
is rejected as a whole and leaves currentNum/currentBytes/currentPercent
exactly as they were. The now-unreachable post-hoc check is removed.
Add TestAddExceedsMaxDoesNotCorruptState covering the corrupted-state
case and that the bar keeps accepting valid progress afterwards.
upstream
dualfroz