Non-rd variance partition: Adjust logic for 32->16 force split.

Lower the threshold for splitting 32x32->16x16 based on average variance,
and add lower bound condition for this split to occur. This prevents
unneccassry splitting for areas with very low variance.

Change-Id: Ibeb33b3d993632c2019f296eb87ef3b7e3568189
1 file changed