Fix for bug #21924 (https://gna.org/bugs/?21924).
This is the failure to output 2D Grace plots for the R20, R20A, R20B, and R1rho0 relaxation dispersion parameters. A simple test for missing data fixed the problem.
Authored by: bugman 2014-04-16
Parent: [r22796]
Child: [r22798]
