Backup file invalid: fix broken Threema backup

Extract backup and ignore Unexpected end of archive error…

7z x threema-backup_*.zip

… and recompress with password.

cd threema-backup_*
7z a -p -mem=AES256 -tzip ../threema-backup_<original_filename>.zip *

Check compression method and encryption (Method = AES-256 Deflate):

7z l -slt threema-backup_<original_filename>.zip