Speed up CLPF when there's nothing to clip
Speed up CLPF when there's nothing to clip

Gives 7% speed-up in the CLPF processing (measured on SSE4.2).

Change-Id: I934ad85ef2066086a44387030b42e14301b3d428

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