improve: expanding threads

Situation: mailbox list shows threads
Action: I click or option-click the triangle to expand the thread
Problem: when the clicked item is at or by the bottom of the list, the expanded items or items below the expanded items disappear below the screen
Suggestion: slide the list up so all listed messages are shown
Justification: when the scrollbar is at the bottom and the sort is to have newest items at the bottom, the list is automatically moved up to show all messages. I am suggesting to extend this behavior to expanding the threads in those circumstances.