Fix for plotting, since the back_calc now can hold more datapoints that cpmg frequencies.
This is because the numpy array has been expanded to the maximum number of points.
Task #7807 (https://gna.org/task/index.php?7807): Speed-up of dispersion models for Clustered analysis.
Authored by: tlinnet 2014-06-16
Parent: [r23990]
Child: [r23992]
