Error when adding an address with unrecognised country

I ran into this when testing address maintenance in the factored-out-code-code version of ui-users in the UIU-278 branch.

The problem is that if you just put "x" for the country, the code barfs when it goes to look that up in the line:

  const countryId = (addr.country) ? countriesByName[addr.country].alpha2 : '';

But because stripes-form is involved and it does something weird with exceptions, the error ("TypeError: Cannot read property 'alpha2' of undefined") just gets thrown away. (I eventually discovered it by tracing the code down into redux-form.)

There's no point fixing this in the current master, so I'll do it on my UIU-278 branch and it'll get merged to master soon. But more worrying is the underlying exception-swallowing problem, which is what concealed this and made it a difficult rather than a trivial problem. I will file a separate issue on that.