Failure to validate form input not handled gracefully

[Hartmut Holzgraefe]

Right now when validation of the "new map request" form fails it will basically just fail with

ValueError at /new/

The view www.maposmatic.views.new didn't return an HttpResponse object. It returned None instead.

instead of providing a more understandable error message back.

This can only really be triggered by entering an invalid notification mail address right now, but still needs fixing.

For one there should be client side validation to try to prevent form submission and give user feedback immediately so that it can be fixed easily.

But also the server side validation needs to provide at least slightly more useful feedback hinting at the actual problem instead of just writing an error log line and not returning a proper HTML page describing the error.