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

[arildm]

Our word picture config doesn't support proper nouns pm. When searching for a proper-noun lemgram, the result is currently just empty:

https://spraakbanken.gu.se/korplabb/#?corpus=abounderrattelser2012&word_pic&search=lemgram|Helsingfors\.\.pm\.1&result_tab=3

We know ahead that we won't be able to show any of the results (even though the /relations call may have hits), so we should show a warning and not perform the call.