This fixes #1755: no error is shown on the client side when an attempt
to register an account receives a 500 Server Error response.

The failure() method in AuthController gets called and tries to do
{errors, reason} = response.data, but this raises a TypeError because
response.data is undefined (because the response didn't have a valid
JSON body), so the client crashes as well.

The fix is to catch this exception on the client side, and show a
generic error to the user.