vp9: Avoid early breakout on slide change
vp9: Avoid early breakout on slide change

For real-time screen content: don't allow early
breakout in nonrd-pickmode on slide change.
Avoid artifacts.

Change-Id: I09c6927a5d85b46ce059ea5954a3719a7362fb99

webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx