[IX] - Feedback when missing segmentations

[txau]

When one or more segmentations are missing, the IX reports it to the user as following:

This leaves the user in a state of confusion since they try to label data and it does not fix the issue. It would be advisable to change the feedback message to:

"Some documents are not segmented yet, please try again later"

[RafaPolit]

Indeed, "No labeled data" is return on a whole sequence of different checks, so there could be labeled data but not files found, etc. So a much better flow and error reporting is needed.