Fix mismatch w/ ext-inter/warped-motion/motion-var
Fix mismatch w/ ext-inter/warped-motion/motion-var

Fixes a mismatch issue with ext-inter+motion-var+warped-motion
due to unset num_proj_ref values.

BUG=aomedia:311

Change-Id: I042551f6c53e8cc005f2133704a03b243c98c12a

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