new_multisymbol: Fix some illegal CDF values.
new_multisymbol: Fix some illegal CDF values.

The probability of several of the symbols used for extra bits for
category 6 tokens, which as far as I can tell are legal to code,
was set to zero, and in one case even negative.

Change-Id: If6bd539b53889d75f974d444d666ed031faf18e0

GrokImageCompression/aom,GrokImageCompression/aom,smarter/aom,smarter/aom,GrokImageCompression/aom,smarter/aom,GrokImageCompression/aom,smarter/aom,smarter/aom,GrokImageCompression/aom,GrokImageCompression/aom,smarter/aom