[Png-mng-security] NULL pointer dereferences in pngerror.c

[John Bowler]

IMO these things should just return if 'png_ptr' is NULL.  It's simple and fast.  If png_ptr is NULL someone (outside libpng) has
done something really bad.  It doesn't seem reasonable to put in a whole load of debugging for such badly broken cases because it
unnecessarily burdens the vast majority of applications.

How about:

if (png_ptr == NULL) return;

throughout.  Alternatively, how about:

if (png_ptr == NULL) abort();

inside png_error.c cases.

John Bowler <jbowler at acm.org>