[Asset Inventory] Cloudbeat panics if SNS topic fetching returns error

[moukoublen]

Describe the bug
When

The problem exists in code: here and here.

While handling ListTopics and returning an error, a break/continue is required and missing. Thus the code attempts to access parts of the nil pointer and panics.

The fix is low-effort and could be backported to the next 8.16.0 BC.