Allow empty folder when exporting bookmarks

[darkdh]

Test Plan

Covered by automatic test
npm run unittest -- --grep="Bookmarks export"

Description

fix #7193

Auditors: @bsclifton, @NejcZdovc

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).