LP#1660059 - Allow for undef value for A/T Processing Group Context Field

LP#1660059 - Allow for undef value for A/T Processing Group Context Field

For an action_trigger.event_definition that uses action.hold_request.sms_notify
as the Processing Group Context Field/group_field, the event processing
shows multiple Perl warnings and the open-ils.trigger process dies.

Tracing this to the relevant code in Trigger.pm shows that there is a
check to make sure that the fieldmapper object actually exists ($node),
but then assumes that the $ident_value (the actual field) is defined/not null.

Adding an additional check fixes the problem.

Signed-off-by: Chris Sharp <csharp@georgialibraries.org>