Prevent divide by zeros in CJBig2_GSIDProc::decode_MMR().
Prevent divide by zeros in CJBig2_GSIDProc::decode_MMR().

Check the image size before attempting to decode.

BUG=538103
R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/1377493005 .

andoma/pdfium,DrAlexx/pdfium,DrAlexx/pdfium,DrAlexx/pdfium,andoma/pdfium,andoma/pdfium,DrAlexx/pdfium,andoma/pdfium