Check for overflow in JBig2 Huffman decoder
Check for overflow in JBig2 Huffman decoder

This CL updates the Huffman decoder in the JBig2 codex to check the low field
does not overflow.

BUG=chromium:675236

Change-Id: I7f5f6fe8329df4ece6f317fac521fe2373686479
Reviewed-on: https://pdfium-review.googlesource.com/2131
Reviewed-by: Tom Sepez <47f022c5217a84c904816c5375403e20a45c37f6@chromium.org>
Commit-Queue: dsinclair <f70dc21b1b6a10340b65b6dcc0bde33e44f9236b@chromium.org>

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