dataio: ensure that MD_WL_POLYNOMIAL with a length of 1 is not saved

Such polynomial happens when spectrum is unknown (ex: the center wavelength is at 0).
We must ensure that it's not saved (as it'd be wrong information).
acq stream: detect if spectrum eff comp data cannot be applied

This can happen on data without spectrum info (eg, poly = 0)
util: fix typo in comment
gui settings: reset filename value if file setter raised an exception

The GUI side (FileBrowser) immediately updates the text widget (which is fair).
If eventually it turns out the file is not compatible, we need to explicitely
put back the current value of the VA.
driver andorshrk: fix length of MD_WL_LIST when resolution changes

the length depends on the resolution of the CCD, not the raw shape.
driver andorshrk: if center wavelength is 0, report empty MD_WL_LIST

Center wavelength at zero mainly means the spectrograph is not correctly set,
let's not report a strange MD_WL_LIST full of 0's, but an empty list to
indicate it's unknown.
util: raise an error if MD_WL_LIST is not the right length

it will be caugth latter on by the GUI, that will conclude the wavelength is unknown.
install: use fake andorshrk in simulated sparc

that allows to test more closely the hardware.
gui: explicitly set WM_CLASS to be able to separate the icons for Odemis and Odemis viewer