dashplayer: Fix green frame issue on session timeout

* Avoid rendering video buffer which signals EOS as it does
  not contain valid video data.

CRs-Fixed: 476333

Change-Id: I10e3a0cb1e2dc9e1574d5e2b05f6339e868ac6fe
Signed-off-by: Hieu Phan <aznrice2k4@gmail.com>