Clarify parser behavior for funky angle bracket addresses

This PR doesn't change any behavior.  It only makes the code more explicit for addresses of the form `blah <blah.co.jp>`.  Currently Mail::Address#address will return nil for these type of addresses.

It's not 100% clear to me that this is intended behavior. If this is a bug I'm more than happy to make another PR that allows us to recognize these types of addresses instead of ignoring them.