boolcoder_test: fix read of uninitialized data
boolcoder_test: fix read of uninitialized data

Only read bits that were actually written.

Change-Id: Id62c52b7804cbfb401e6e7388201406bc899ea5d

luctrudeau/aom,luctrudeau/aom,mbebenita/aom,smarter/aom,mbebenita/aom,mbebenita/aom,luctrudeau/aom,GrokImageCompression/aom,mbebenita/aom,smarter/aom,luctrudeau/aom,GrokImageCompression/aom,mbebenita/aom,luctrudeau/aom,GrokImageCompression/aom,smarter/aom,smarter/aom,luctrudeau/aom,smarter/aom,mbebenita/aom,GrokImageCompression/aom,mbebenita/aom,smarter/aom,mbebenita/aom,GrokImageCompression/aom,GrokImageCompression/aom,mbebenita/aom