[backport#14478] Show error to user when corrupt wallet unlock fails

Summary:
Better error message for user when corrupt wallet unlock fails (MeshCollider)

Pull request description:

Mentioned here: https://github.com/bitcoin/bitcoin/issues/14461#issuecomment-429183503

Current behavior is to assert(false) and crash, only info is printed in the log. This shows the message to the user before abort() instead.

https://github.com/bitcoin/bitcoin/pull/14478/commits/b4f6e58ca5a74225b6db9deb3ffe1ce3ab19a790

Backport of Core PR14478

Test Plan:

ninja check

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D7312