Don't initialize first pass costs for a number of symbols where first
pass probabilities aren't initialized.
As a side effect, an illegal read in the ANS experiment is fixed.
https://bugs.chromium.org/p/webm/issues/detail?id=1089
Change-Id: I97438c357bd88f52f5a15c697031cf0c3cc8f510
Brings the following commits to vp10:
269428e Tie the bit cost scale to a define.
d13385c Switch to 9-bit rate cost constants built on a 256 probability denominator.
ad43a73 Fix a signed overflow in vp9 motion cost.
1c9b091 Fix some interger overflow errors
fac947d Restore previous motion search bit-error scale.
Change-Id: I598ba7ee7efcde18439c31dfa96b86cbf297a580
Geza Lore
Alex Converse
Yaowu Xu
Jingning Han