Skia: bug fix for SkBitmapProcState_shaderproc.h

Take care of "dx" being 0 case

Change-Id: Ie492c0454d6c8876ea9bb48e911de77cc78a8e98
Merge pull request #1 from CyanogenMod/cm-11.0

Skia: bug fix for SkBitmapProcState_shaderproc.h