Fix zero-fill logic in graphs

Add zero-padding to the end of of the graphs up to the present time
so they continue to move left even if there are no new hits (the
current behavior shows a graph from the first to the last hit).

Also, fix an OBOB with the zero-fill between hits.

Change-Id: I1938b779e0c5c383f4a7b1eb9a63dd5401cc9889