Prevent rewriting the encrypted file if decryption fails
Add missing sha1 import on known_hosts.py
Bump version to 1.5.4.1, includes fixes for:

* SHA1 import for known_hosts (e9d7476c)
* Empty vault on password failure (issue #6617, b8f627d1)

Signed-off-by: Matthew Schick <matthew.schick@gmail.com>