Fix reply for Ordinate Axis

[stuwilkins]

During testing at IOS, we found that our analyzer when presented with the command

?0145 GetSpectrumDataInfo ParameterName:"OrdinateRange"

Only returns

!0145 OK: ValueType:double Unit:""

Missing are the optional Min: and Max: values. The change in stuwilkins/specsAnalyser@d939df1 traps the case where the units are a null string and does not continue (returns asynError). There is probably more of an issue with the function cleanString() which throws an exception to the above response.

[stuwilkins]

Note: fixed this a different way with stuwilkins/specsAnalyser@06dc7ab

Now, it doesn't call cleanString() if the string is ""