Previously, like the Go code, calculating the zero polynomial would fail
for very lare numbers of missing indices. For example, 253 missing with
a domain size of 256 - this is where the number of partials flips from 4
to 5 and more working space is needed.
With this commit, the zero polynomial can be calculated right up to all
but one of the indices missing. The case with all indices missing
doesn't work as the return data is too large, but the solution is known
to be `x^width - 1` in case we need to know.
