Fix a bug for very low resolutions
Fix a bug for very low resolutions

Don't call GPU execution kernels for the last few sub-frames, when the
global workgroup size is zero

Change-Id: I70b324110966cccb10bcea78417ee3ce9d755de0
ittiamvpx/libvpx,ittiamvpx/libvpx,ittiamvpx/libvpx,ittiamvpx/libvpx,ittiamvpx/libvpx,ittiamvpx/libvpx