it turns out that
    soffice --headless --convert-to pdf tdf89833-2.xlsm
semi-reliably fails with
stl concept checking "Error: attempt to compare a dereferenceable
iterator to a singular iterator"
because we are modifying ScPatternAttr all over the place, which messes
with the sorted list in the pool.

Change-Id: Id662ac32b024c2c60b32b6cf433c12deb614f0fa
Reviewed-on: https://gerrit.libreoffice.org/71677
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>