Properly show conversation settings

... when the backing shortcut is missing, so users can change
notification settings when the shortcut hasn't yet been recreated by the
app when setting up a new device

Test: Robotests (confirmed that the 2 controllers that used
mConversationInfo already tested for null), manual
Fixes: 203991823

Change-Id: I477c6b0aef0d978767788cbfc1bfadea4d36cda8