[MlMt] Can't edit pasted in To address in composer

[Eric Sharakan]

The subject pretty much says it all - once I paste an address into the 
To: field of the composer, it gets a box drawn around it with a dropdown 
menu arrow on the right.  At that point, it's impossible to edit the 
address, I can only delete it.

Running r5726 on Catalina 10.15.7.

Thanks.

-Eric