Comment 5 for bug 1652100

Mc and I figured out why the commit mentioned in #3 regressed performance.

I just committed a fix in
  https://gitlab.com/inkscape/inkscape/commit/8052d8eadcfa0201ee0ec7a1230bbf91c470da79
which should restore previous performance.

As this shows the data structure used here is not ideal some further optimizations in this code might be possible in future.