Fixed Import External Data become inaccessible if in-processing importer has been deleted

[sonnb]

If we stop current custom import progress, remove that importer (uninstall addon). Import External Data page would not be able to be used as it would throw an error indicates that the importer does not exist.

I think we should check for this case and ignore it?

 

[Mike]

I've changed it to through an error, though you could still always simply tell it to start a fresh import.