LP#1752753: Guard against invalid timezone

LP#1752753: Guard against invalid timezone

If the lib.timezone org setting is not a valid timezone, attempting to
use it can result in an internal server error in the OPAC.  Let's handle
the error with try/catch instead.

To test
-------
1. In Library Settings Editor, edit the "Library time zone" setting for
   Example Branch 1, setting the value to something that's not the name
   of a time zone (like "invalid" or "UTC-07:00").
2. In the OPAC, retrieve a record with holdings at Example Branch 1.
    You will get an Internal Server Error.
3. Edit the library setting to use a valid timezone name, like
   "America/Vancouver".
4. Retrieve the same record again. This time, the record will display
   properly.
5. Apply the patch and repeat steps 1 and 2; this time, there should
   be no internal server error.

Signed-off-by: Jeff Davis <jdavis@sitka.bclibraries.ca>
Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>