Do not exit on exception resolving addresses to notify

[omoerbeek]

Fix #7646.

It might not be the right place, though, but it prevents fatal exception on
unparseable A (or AAAA) addresss for nameserver addresses needed
to send notifies.

Checklist

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• read the CONTRIBUTING.md document
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• included documentation (including possible behaviour changes)
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• added or modified regression test(s)
• added or modified unit test(s)