Accept that in --batch mode. Also in batch mode don't send the 0th arg. Related discussion: https://github.com/harfbuzz/harfbuzz/pull/3102
This seems to have been carried over from the Indic shaper, but Uniscribe enables it by default. See https://github.com/harfbuzz/harfbuzz/issues/2213#issuecomment-686062915