fdo#73352 don't crash if clearWarnings throws an SQLException

Change-Id: If67bda43589834e4c922056145bc60884728cb8a
Reviewed-on: https://gerrit.libreoffice.org/9592
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>