fix filtering auto-adjustment

the min-distortion was quite too low. And we were also
considering the fully skipped macroblocks (nz=0) in the stats.
We need to have at least *some* non-zero dc coeffs (nz=0x100XXXX).

Fix also two typos in StoreMaxDelta: the v0/v1 comparison was wrong,
and the DCs[] coeffs are actually already in ZigZag order.

Change-Id: I602aaa74b36f7ce80017e506212c7d6fd9deba1f
1 file changed