[BUGFIX] Cannot localize message when uploading in Frontend

When files are uploaded from the Frontend, e.g., using
https://gist.github.com/xperseguers/9076406, the resize message cannot
be prepared as a Backend context is not available.

Change-Id: I33f1707c04dd59fe38f94fc98ec3b31070d2bc72
Fixes: #56090
Reviewed-on: https://review.typo3.org/27699
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers