Fix bug where longpress stops working

For shelfless dismissal, create NotificationMenuRow as empty menu
instead of leaving it null (which skips longpress guts open)

Fixes: 173252412
Bug: 172289783
Test: visual - longpress works for hun/min/expanded notifs, in
shade/home/lockscreen, with flag disabled and enabled

Change-Id: I6d2254da6545bcf1278cc3c90e2fb18d30b81b74