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

Change-Id: If67bda43589834e4c922056145bc60884728cb8a
Reviewed-on: https://gerrit.libreoffice.org/9591
Reviewed-by: Lionel Elie Mamane <lionel@mamane.lu>
Tested-by: Lionel Elie Mamane <lionel@mamane.lu>