ChangeScreen2: Fix position of ReplyBox

Currently, ReplyBox is misplaced or even missing when the page is not
scrolled to the top.  Fix by scrolling the page to the top before
showing the PopupPanel.

Change-Id: Iea04ac40855a2588fc6eec9adca46fd11fcf937a
Merge "ChangeScreen2: Fix position of ReplyBox"