Loading a map page with an invalid `q` parameter raises differing errors in some browsers

[jwalgran]

We do not handle invalid values of the q query string parameter on the map page. Loading the {url_name}/map page with a q argument like q={"mapFeature.geom":{"IN_BOUNDARY":"31225 produces a syntax error in Firefox on macOS and IE 11 on Windows 7.

https://rollbar.com/Azavea/OpenTreeMap/items/2826/
https://rollbar.com/Azavea/OpenTreeMap/items/2827/

Low priority because the app does not produce broken JSON values. This looks like a copy/paste error