Since the previous call would throw if there was nothing to be assigned
to the value.

Idea from tml.

Used the following script to find places:

    git grep -A3 -n UNO_QUERY_THROW | grep -B3 -F 'is()'

Change-Id: I36ba7b00bcd014bdf16c0455ab91056f82194969
Reviewed-on: https://gerrit.libreoffice.org/55417Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Tor Lillqvist <tml@collabora.com>
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>