Word picture: More appropriate message on backend errors

[janiemi]

When the word picture search fails due to a backend error, the word picture result tab shows the message “Could not generate a word picture from you search. Only 'Simple search' on one word or lemgram is supported.”, even if the search is of the kind for which word picture is supported.

This currently happens for this Korp search, which at present causes a GreenletExit in the backend (see spraakbanken/korp-backend#10). Even though that situation might be temporary, I think the frontend should show a different error message.

[majsan]

Agree!

[arildm]

I cannot reproduce this now, but backend errors of that kind should be visible now since #97 was fixed.

The given example search instead shows an empty result, and that is because our word picture config doesn't have anything for proper nouns (pm). That should be fixed, but since it doesn't match this issue description I created a new issue for that:

• Prevent word picture search if config doesn't support the lemgram's POS #421

@janiemi Could you check if this is still relevant and add a new example search?

[janiemi]

@arildm, I could not reproduce this any longer, either. Neither could I come up with another word picture search that would result in a backend error. I thus suppose you can close this issue.