"Return to impact" button on DYFI form doesn't go to the right place

[vinceq-usgs]

After filling out an Unknown Event form, the "Return to Impact" button goes to:

/earthquakes/eventpage/null/impact

which loops back into the form.

For users on small screens, the "Return to Impact" is the most obvious way to exit the form, but the Impact screen is not really useful for most users--- return to the DYFI page or Overview page instead?