Add wtf log if notification panel height is NaN

NotificationPanelViewController#getMaxPanelHeightNonBypass() is the one
place where we aren't explicitly checking for NaN where it could be
introduced into PanelViewController mExpandedFraction.

Test: manual
Bug: 160688163
Change-Id: I3e5047295085cd61c3ceebe456c6560b28f616f7