files_encryption: Migration from 4.5.11 to 5.0.7-pre leads to 0byte files on view/download

[ghost]

Expected behaviour

Migration from OC 4.5.11 with the old files_encryption app to the new files_encryption app in OC 5.0.7-pre should convert all existing files to the new app.

Actual behaviour

Migration from OC 4.5.11 with the old files_encryption app to the new files_encryption app in OC 5.0.7-pre won't convert all existing files to the new app.

Some files are good and can be downloaded / viewed. Others not and downloading those files leading to a 0 byte download.

The files which have this problems don't have a a keyfile in:

data/$username/files_encryption/keyfiles

Additional to the errors in the owncloud.log i've seen many of the error messages described in #2566 but i'm not sure if this is connected to this problem.

Steps to reproduce

1. Have an old OC 4.5.11 with files encrypted with the old files_encryption app
2. Make the changes in this PR to fix migration problems: https://github.com/owncloud/core/pull/3504/files#L1R616
3. Doing a upgrade to OC 5.0.7-pre

Server configuration

Operating system: Debian Wheezy

Web server: NginX 1.2.26

Database: MySQL 5.5.x

PHP version: 5.4.14

ownCloud version: 4.5.11 and 5.

Logs

Web server error log

Nothing useful in here

ownCloud log (data/owncloud.log)

 {"app":"hook","message":"error while running hook (OCA\\Encryption\\Hooks::login): Cannot mutliKeyEncrypt empty plain content","level":3,"time":1369925242}

Browser log

Nothing useful in here

[ghost]

Closing this for now because it should be fixed with #3552.