Add missing fallback blending to SkA8_Shader_Blitter::blitMask()

Similarly to SkA8_Shader_Blitter::blitAntiH() and SkA8_Shader_Blitter::blitH(), blitMask() should handle a missing SkXfermode gracefully.

R=reed@google.com

Author: fmalita@chromium.org

Review URL: https://chromiumcodereview.appspot.com/22867008

git-svn-id: http://skia.googlecode.com/svn/trunk@10743 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed