Fixed the wrong timestamps issue about camera recording

On emulator, the camera video recording crashes randomly.
It's caused by wrong timestamp when encoding the video frame.
The element of the vector is erased before accessing it.
Therefore, when reading the timestamp from the element,
the memory of the element has been changed.

Change-Id: I9750417fbb9dc4697ccae1e78e286b23925d3764

Signed-off-by: Panfeng Chang <panfengx.chang@intel.com>
Signed-off-by: Jun Tian <jun.j.tian@intel.com>