Fix for bug #21499 (https://gna.org/bugs/?21499), the failure of the rdc.write user function.
The rdc.write user function fails for back-calculated RDC data. The fix was to handle the missing interatom.rdc_data_types variable.
Authored by: bugman 2014-01-17
Parent: [r22024]
Child: [r22026]
