Please do not turn a 400 error into a 500 error

[olivier65]

In the event of a 400 error the search widget shows the ERROR_500 message, which was very confusing at first: I thought maybe the Pelias server was undergoing maintenance! You should implement an ERROR_400 string since it is very easy to get a 400 error, e.g., a space between layer types (such as "address, venue" instead of "address,venue") or any other typo in the geocoder options will do.