libstagefright: Fix a video lag bug after audio reached EOS.

http://git.insignal.co.kr/samsung/exynos/android/platform/frameworks/av/commit/?h=exynos-jb&id=da4104e5f934633b4ba7fda06bc9ef3ba0f85a31

Change-Id: I14931cad92df48e1233c5a8a704bb18585b1795a