Fix a bug in deciding ref frame context in ext-refs
Fix a bug in deciding ref frame context in ext-refs

Change-Id: Ie58b98baa870c5d2a5b7193f8fe4f84fd7ec6c16

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