Merge to XFA: Fix NULL pointer dereference in CPDF_InterForm.

BUG=537772
TBR=tsepez@chromium.org

Review URL: https://codereview.chromium.org/1387703002 .

(cherry picked from commit 4f277fc8d41303cbf007335dfbbff60b81fffde0)

Review URL: https://codereview.chromium.org/1380603006 .
2 files changed