Update copy of safe_math_impl.h to take a fix from upstream:
Update copy of safe_math_impl.h to take a fix from upstream:

Fix a division by zero when multiplying 0 * y with SafeNumerics.

BUG=488302
R=jschuh@chromium.org

Review URL: https://codereview.chromium.org/1126243007

was4444/pdfium,bradh/pdfium,azunite/pdf_clone,wwxxyx/pdfium0,DrAlexx/pdfium,nathanstitt/pdfium,chenjian-rits/HelloWorld,klokantech/pdfium,klokantech/pdfium,rouault/pdfium,chenjian-rits/HelloWorld,DrAlexx/pdfium,chenjian-rits/HelloWorld,andoma/pdfium,azunite/pdf_clone,bradh/pdfium,wwxxyx/pdfium0,azunite/libpdfium,azunite/pdf_clone,bradh/pdfium,was4444/pdfium,nathanstitt/pdfium,pwaller/pdfium,pwaller/pdfium,azunite/libpdfium,azunite/libpdfium,wwxxyx/pdfium0,was4444/pdfium,klokantech/pdfium,nathanstitt/pdfium,andoma/pdfium,rouault/pdfium,andoma/pdfium,DrAlexx/pdfium,andoma/pdfium,pwaller/pdfium,rouault/pdfium,azunite/libpdfium,DrAlexx/pdfium,was4444/pdfium