Qt: pass clientmodel changes from walletframe to walletviews

Summary:

We currently don't pass clientmodel changes from the walletframe to the walletviews leading to possible invalid access during shutdown because all walletviews miss the nullifying of the clientmodel.

This is a backport of Core PR18091

Test Plan:
ninja && src/qt/bitcoin-qt -regtest
Open console
generatetoaddress(1000,getnewaddress())
Quit bitcoin-qt

Before this patch: segfault
After this patch: graceful shutdown.

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D8740