NuPlayer: Fix incorrect time update for pause followed by seek, resume

 -During pause, seek and resume sequence progress bar moves
  back to paused time stamp and then come back to actual seek
  position on resuming.
 -On resuming NuPlayer renderer gives last pause position if
  getcurrent position is called before state is set to running.
 -reset the pause position during flush to fix the above scenario.

Change-Id: I75e0acab0bff9851cd223645c461d6d8bb0633c1