SaveSPE should place -10^30 in the spectra of masked detectors

[Steve Williams]

The SPE file specification states that masked spectra should have Y values of -10^{30 and an error of zero. Jon Taylor told me that their mslice software needs this}

[Steve Williams]

(In [4002]) SaveSPE() now flags spectra whose detectors are all masked as invalid. All bins in their spectra take the flag value -10^{30 fixes #1140}

[Steve Williams]

(In [4003]) Fixes the SaveSPE Deoxy Gen problem refs #1140

[Steve Williams]

To be consistent LoadSPE needs to mask detectors and convert the -10^{30 flag value to not-a-number. Also SaveSPE should convert not-a-number to -10}30

[Steve Williams]

(In [5075]) LoadSPE should recognise and convert the SPE file -10^{30 flag value re #1140}

[Nick Draper]

Moved to verify state

[Michael Whitty]

verified in #5878 - though some files won't load in LoadSPE