wireguard: T7087: Fix vyos-domain-resolver failing if no wireguard interfaces defined

[Embezzle]

Change summary

T4930 has introduced a bug where if no wireguard interfaces are defined, the vyos-domain-resolver process exits with failure. This PR implements a check in vyos-domain-resolver to see if output of dict_search_args is NoneType before attempting to iterate.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

https://vyos.dev/T7087
https://vyos.dev/T4930

Related PR(s)

• T4930: Allow WireGuard peers via DNS hostname #4200

How to test / Smoketest result

Test Steps

1. Configure a domain-group, whilst having no wireguard interfaces configured:

vyos@vyos# set firewall group domain-group test address vyos.dev
vyos@vyos# delete interfaces wireguard

2. Check vyos-domain-resolver starts correctly:

vyos@vyos# sudo systemctl status vyos-domain-resolver
● vyos-domain-resolver.service - VyOS firewall domain resolver
	 Loaded: loaded (/lib/systemd/system/vyos-domain-resolver.service; disabled; preset: enabled)
	 Active: active (running) since Sat 2025-01-25 12:45:18 GMT; 10s ago
   Main PID: 8272 (python3)
	  Tasks: 1 (limit: 1086)
	 Memory: 38.1M
		CPU: 290ms
	 CGroup: /system.slice/vyos-domain-resolver.service
			 └─8272 /usr/bin/python3 -u /usr/libexec/vyos/services/vyos-domain-resolver

Jan 25 12:45:18 vyos systemd[1]: Started vyos-domain-resolver.service - VyOS firewall domain resolver.
Jan 25 12:45:18 vyos vyos-domain-resolver[8272]: VyOS domain resolver
Jan 25 12:45:20 vyos vyos-domain-resolver[8272]: interval: 300s - cache: False
Jan 25 12:45:20 vyos vyos-domain-resolver[8272]: Updated 1 sets in firewall - result: 0
Jan 25 12:45:20 vyos vyos-domain-resolver[8272]: Updated 0 sets in nat - result: 0

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

[github-actions]

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No issues in PR Title / Commit Title

[github-actions]

CI integration 👍 passed!

Details

CI logs

• CLI Smoketests (no interfaces) 👍 passed
• CLI Smoketests (interfaces only) 👍 passed
• Config tests 👍 passed
• RAID1 tests 👍 passed
• TPM tests 👍 passed