[backport#15917] wallet: Avoid logging no_such_file_or_directory error

Summary:
wallet: Avoid logging no_such_file_or_directory error (João Barbosa)

Pull request description:

Avoid logging `IsBerkeleyBtree: No such file or directory ...`. The result of `IsBerkeleyBtree` is the same since `fs::file_size()` returns 0 for non existent files.

Fix #15912.

Backport of Core PR15917

Test Plan:

ninja check

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7351