uplift(beta): crash when opening placeholder folder

[rafaeltonholo]

This PR uplifts #9716 to beta, fixing the placeholder account crash issue.

[thunderbird-botmobile]

Thank you for your uplift request! Please add a comment with the following approval request template filled out.

[Approval Request]
Original Issue/Pull request: #9644/#9716
Regression caused by (issue #):
User impact if declined: The app crashes as soon as the user taps in the placeholder folder.
Testing completed (on daily, etc.): daily, main, beta (local build based on this branch)
Risk to taking this patch (and alternatives if risky): Folder with nested folders could not expand or open in case the account id is null, which is unlikely to happen.

[platform34]

I see this was lifted to 13.0B5 release. Is it possible to also uplift #9743 "fix: remove Gmail prefix when updating folder list" to beta. It's the secondary part to this fix. The full resolution could then be tested in beta, instead of the partial fix.