libstagefright: Fix timestamp corruption during offload playback

-Timestamp gets corrupted at EOS of offload playback.
-This happens because the number of samples played returned from
 HAL could be zero if playback has reached EOS and if compress
 handle is invalid / closed.
-If HAL has posted EOS  avoid the update of real time and media
 time with the timestamp from HAL.

CRs-Fixed: 570368
Change-Id: I5ea75f4eda1df0c110bce780e50e3c8ae9b4cd85