Missing files give an error of "Do not know how to read file extension"

[dschwoerer]

It would be nice to give a more useful error:

• Expected file name but got a folder
• File does not exist

Maybe some more things we should check ... ?

[ZedThree]

Is it just a matter of putting this line:

xBOUT/xbout/load.py

Line 746 in 4670160

filetype = _check_filetype(path)

after the checks on filepaths in that function?