Crash (segfault) when zooming in / out of blurred region

Merged from https://bugs.launchpad.net/inkscape/+bug/1666550

Inkscape crashes with a segfault if I create a rectangle, add blur to it and then rapidly zoom in and out.

Inkscape version: 15537 Platform: Debian Testing

I reproduced it 3 times with the attached SVG with "Release WIth Debug Information" build and then once more with a "Debug" build.

blur-crash.svg blur-crash3.txt