Resolve to 0 if resolver is set but addr isn't

[danfinlay]

Instead of to owner.

Per MetaMask/metamask-extension#1427

[kumavis]

does 0 imply an error or would it be better to explicitly error. dont want to accidentally send to 0.

[danfinlay]

Yeah we'll just throw. I believe we actually throw when an address resolves to 0 already, but just to be clear, we'll throw.