Add guards for uncatched errors

[WeeJeWel]

Without this code, the following exceptions happen:

TypeError: Cannot read property 'priority' of undefined
    at State.record (/var/app/current/node_modules/modern-dnsd/encode.js:169:37)

Error processing request TypeError: Cannot read property 'map' of undefined
    at State.record (/var/app/current/node_modules/modern-dnsd/encode.js:160:29)

It seems that the initial object is wrong, but I have too little knowledge of this project to understand how to fix that.

[ansuz]

I also have too little knowledge of this project to understand how to fix it.

PRs fixing the deeper issues are very welcome!