Skia: bug fix for SkBitmapProcState_shaderproc.h

Take care of "dx" being 0 case

Change-Id: Ie492c0454d6c8876ea9bb48e911de77cc78a8e98
Merge branch 'cm-11.0' of github.com:CyanogenMod/android_external_skia into tfkk-4.4