wallet: Catch filesystem_error and raise InitError

Summary:
Fixes #13754 by restoring the previous behaviour

Backport of Bitcoin Core PR13876
https://github.com/bitcoin/bitcoin/pull/13876

Test Plan:

make check

Reviewers: Fabien, #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D3987