Add more diagnostic when server is not recognized

[prjemian]

@padraic-shafer reports (on Mattermost)

that all of the NSLS2 beamline catalogs are unsupported right now.

...

I see...it does not like that the catalogs do not specify any specs.

gemviz/gemviz/mainwindow.py

Lines 102 to 106 in ffb2e5e

	try:
	spec = specs[0]
	spec_name = f"{spec.name}, v{spec.version}"
	except IndexError:
	spec_name = "not supported now"

INFO:gemviz.mainwindow:Status: Selected catalog 'amx'.
DEBUG:gemviz.mainwindow:specs=ListView([])
DEBUG:gemviz.mainwindow:structure_family=container
INFO:gemviz.mainwindow:Status: catalog 'amx' is 'not supported now'

Thanks for the report @padraic-shafer! We can report more details in such situations. In this case, we'd report that there were no specs available. Documentation (also TBA) could inform what are these specs, for example.