HPCC-11679 Catch exception in connection destructors

Avoid problems with exceptions being generated during clearup,
that causes problems if clearing up to handle an original exception.
Catch exception in connection beforeDispose and generate a log entry
only.

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #6061 from jakesmith/hpcc-11679

HPCC-11679 Catch exception in connection destructors

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>