Fixed EZP-20687: Existing file path outside the vardir throw an exception

Link: http://jira.ez.no/browse/EZP-20687 

Logs an error instead when such a path is encountered. This is just to avoid
a fatal error. These inconsistencies should be fixed using the legacy update
script update/common/scripts/5.1/fiximagesoutsidevardir.php.

# See also
https://github.com/ezsystems/ezpublish-legacy/pull/621 for testing & legacy pull request