Bug - Second wallet connection to existing Monerium account.

Summary

Currently, a user that has successfully gone through the Monerium flow once, cannot register another wallet to the same Monerium account, and the app will fail without proper handling this case.

Detailed explanation

Since we cannot detect a user that has already done the Monerium KYC only by it's address, nor can we know the account that the user will use during the authentication, we cannot prevent a user attempting to connect a second address to our app.

From the user's perspective, the flow will go similarly to the first time only without any kyc data asked, and the flow will be "successful". On the subsequent register step, the backend won't be able to find the IBAN associated with the newly connected wallet, and the app will crash.

The root cause of this issue, is that only one IBAN can be associated with one person by default.

This issue is related to this ticket.

Start by reproducing the second-wallet Monerium flow and trace the subsequent register step, where the issue says the backend cannot find the IBAN. Review related issue #884 for context. Done means a second wallet attempt is handled without the app crashing, with an appropriate outcome for the missing IBAN case.