Fix saving :addresses

Running 1.0.2 with the managesieve plugin I noticed that I could no longer save additional addresses with vacation-type rules. Values entered into the field(s) just get discarded. I looked into the code and it appears that the value in `$addresses` actually looks like

~~~php
(
    [0] => Array  
        (
            [0] =>   
        )
  
    [1] => Array
        (  
            [0] => email@address
            [1] => second@address
        )
  
)
~~~

So `array_shift` just returns an empty array every time.

From git log I could not immediately figure out when this broke, but this PR fixes it for me.