Comment 2 for bug 271401

Attaching patch (applies to inkscape-0.47~pre4, but I'm sure it's simple enough to paste the code into any version).

The problem is that libpng uses setjmp/longjmp for error handling. Inkscape was not calling setjmp, so libpng was taking the default method of handling errors: abort.

This is my first inkscape patch and I am unfamiliar with the codebase, so please check it over.