Fixed extractPubkeys

[rrrooommmaaa]

This PR fixes ContactStore.extractPubkeys()

close #3659

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Tests (delete all except exactly one):

• Tests added or updated

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To be filled by reviewers

I have reviewed that this PR... (tick whichever items you personally focused on during this review):

• addresses the issue it closes (if any)
• code is readable and understandable
• is accompanied with tests, or tests are not needed
• is free of vulnerabilities
• is documented clearly and usefully, or doesn't need documentation

[tomholub]

Good for this particular PR, but it would be good to test this with UI tests (click the export all button, and expect pubkeys to come out).