if we're going to throw the base class of the exception hierarchy,
we can at least put a useful message in there to make the source a little
bit easier to locate.

Change-Id: I2f3106c99ba25125eacef8fa77e2f3a2c89f2566
Reviewed-on: https://gerrit.libreoffice.org/42968Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Julien Nabet <serval2412@yahoo.fr>