New image saved with wrong date when no new detection

[KohajdaG]

When the image_processing.scan fired, but no lpn was recognized, the last_detection attribute not updated (because no new detection), but the image was saved with that wrong date.

In the attached image, the actual time is 17:56:34 (when the scan fired), but the recognisation was not successful and the image was saved with the last successful last_detection date (15:14:55), so it overwiev, the previus one which was the correct one for that time.