Fix unit test failure in obmc exp
Fix unit test failure in obmc exp

Properly restore the rate cost in the inner search loop of obmc
prediction. This avoids unexpected encoding behavior. It fixes
the unit test failure in obmc experiment:

AltRefForcedKeyTestLarge.Frame1IsKey/2

Change-Id: I667b219dfcf2f2c63d9d984900ed3cfd10c354bd

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