Fix build error when building Android in Release mode with -O2.
Fix build error when building Android in Release mode with -O2.

This fixes the folowing error...

../../../src/pdf/SkPDFShader.cpp: In function 'void gradientFunctionCode(const SkShader::GradientInfo&, SkString*)':
../../../src/pdf/SkPDFShader.cpp:69:19: error: array subscript is above array bounds [-Werror=array-bounds]

Review URL: https://codereview.chromium.org/13471011

csulmone/skia,csulmone/skia,csulmone/skia,csulmone/skia