UI Template - Ensure passthru is set at runtime, if not configured in Editor

[joepavitt]

Description

Seeing issues around warnings and deployment problems with ui-template:

• https://discourse.nodered.org/t/dashboard-2-ui-template-config-error/84785
• Dynamic Properties - Ensure consistency on how dynamic classes (and other props) are set #497 (comment)

Can't see any reason why they're occurring, they're not marked as required fields, and there is an explicit check to see if the passthru field exists before any logic using it is considered.

The only option I can possibly think of is the undefined nature of passthru, so I've added a catch here at runtime.

Checklist

• I have read the contribution guidelines