https://bugs.kde.org/show_bug.cgi?id=333763 shows that the Xapian database constructor can throw an exception, which is not handled at the moment. This patch wraps all Xapian-related stuff in Baloo::FileFetchJob::doStart() in a try {...} block and catches all exceptions.

The alternative would be to only add a catch statement for the Xapian::DatabaseOpeningError which seems to be thrown according to the bug report, provided that we can be 100% sure that no other exceptions can be thrown there. IMHO, a library that uses external libraries that can throw exceptions should try as hard as possible to catch all exceptions.

Unit tests still pass.