encoder/temporal_filter.c: fix ubsan warnings
encoder/temporal_filter.c: fix ubsan warnings

Change-Id: I30fa12202f29524984647d97ca363cb40bc68208

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