NuPlayerRenderer: Update position of AV stream even after audio EOS

For AV streams with shorter audio, anchorTime does not update beyond
audio EOS causing MediaPlayer.getCurrentPosition to return the same
fixed value (progress bar does not update).
Allow updating the current position in renderer beyond the anchorTime
to update the player's position if audio stream is present.

CRs-Fixed: 808073

Change-Id: I75625d24a6c155ff12f27fd0848503657e9219aa