...so that displaying a (non-translated) error box upon BE_UNO_SERVICEMANAGER
works after all.  Augment the error text with an exception message where
appropriate.  This allows to revert fdfb7a3c
"Related fdo#51252: Report uncaught exceptions with MessageBox on Windows" as
that was to catch and display failures from instantiating the service mgr.

Change-Id: I049a38e95342634796eb0e940e2ee8e55193c9d3