handle nullptr SharedString in ScQueryEvaluator (tdf#149679)
This may be the case if the string comes from ScMatrix::Get()
for ScMatValType::Empty.
Change-Id: I35013449611bf7ffd1bc74e023d76597af010724
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/136347
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>
(cherry picked from commit
ba59bd11521373f800c6b718e7e21439c1452e84)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/136376
Reviewed-by: Adolfo Jayme Barrientos <fitojb@ubuntu.com>