Fix for bug #21460, the failure of relaxation dispersion due to incorrect spectrometer information.
This is the bug https://gna.org/bugs/?21460, reported by Min-Kyu Cho (min-kyu dott cho att live dot
com).
There was only one place in the dispersion analysis which failed due to a spectrometer frequency not
containing any relaxation data - in the insignificance testing in the auto-analysis.
