The new API requires an extra array member at the very end,
which old API users did not do.
This disables in-place RDFT transforms and instead
does the transform out of place by copying once, there shouldn't
be a significant loss of speed as our in-place FFT requires a reorder
which is likely more expensive in the majority of cases to do.
Cherry-picked from
90adef99ca
Differential Revision: https://phabricator.services.mozilla.com/D203388
