Resolve codec issue between tile-groups and ext-refs
Resolve codec issue between tile-groups and ext-refs

This fixes the coding failure when both tile-groups and ext-refs
are turned on. It clears the nightly-run unit test failure.

Change-Id: Idb67580ebe3ef625cf3ab18dcf7a274db4dacab3

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