[FIX][JUNGFRAU][CORRECT] Index first cell for single cell corrected data

A fix for a bug found while using automated tests.

In case of single cells the plotting arrays should be of shape [trains, x, y] by indexing the cell.

Description

How Has This Been Tested?

Testing CALLAB collected JF runs. and running the notebook interactively.

Relevant Documents (optional)

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• Test with old data

Reviewers

@schmidtp @danilevc @kluyvert