Fixes #26273.
This crash happens with a very deep stack trace that is caused by
destroying shared media layer on Go to Message click, which starts
destroying Media::ListWidget, which destroys Ui::PopupMenu, which is
a window, so when it destructs it triggers a sync repaint of the main
window (by a system event), which tries to render the new messages slice,
which starts a photo download, which calls an item repaint in Data::Session,
and the semi-destroyed Media::ListWidget is still subscribed to the
item repaint requests and tries to repaint and crashes there.
The fix is to destroy all session-related subscriptions before the PopupMenu.
f671897a4d