wallet: Fix bug when just created encrypted wallet cannot get address

Summary: This is a backport of core#20230

Test Plan:
Run src/qt/bitcoin-qt -regtest.
Create a new encrypted wallet.
Check on the "Receive" tab that the "Create new receiving address" button is not disabled.

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10713