Restore a width check that was removed from png.c (CVE-2015-0973)

Backported from upstream commit 6d8c88177a. Note that this update
from beta3->rc1 contained one other (accidental) change to pngrutil.c
that was subsequently reverted in rc2.

Note that the code around this has moved around and changed quite
a bit since 1.6.10.

bug: 19499430

(cherry picked from commit f4435dfcdb5733f9c340492cc7fcac88a13f6ebd)

Change-Id: Ifde854718c98b92c5846dda62d9fddb5d7fcf6da
1 file changed