Check for LS2 Hub error before processing callbacks

:Release Notes:
Add tests for hub error message when processing callbacks to avoid crashes
in LS2 when passing NULL'ed elements in this case.
Also added additional logging.

:Detailed Notes:

:Testing Performed:
Tested to ensure the change does no harm.
mini-BAT

:QA Notes:

:Issues Addressed:
[GF-37898] Excessive crashes occuring in LS2: LSTransportMessageGetSenderServiceName

Open-webOS-DCO-1.0-Signed-off-by: Roger Stringer <roger.stringer@lge.com>

Change-Id: Ife5c4b97b93530bb07f44ea1313ba7ec94ebe060
Reviewed-on: https://g2g.palm.com/3444
Reviewed-by: Build Verification
Reviewed-by: Eric Blade <eric.blade@lge.com>
Reviewed-by: Roger Stringer <roger.stringer@lge.com>
Tested-by: Roger Stringer <roger.stringer@lge.com>