xpdf: uninitialized Gfx::parser pointer dereference

The Gfx::getPos function in the PDF parser in xpdf before 3.02pl5, poppler 0.8.7 and possibly other versions up to 0.15.1, CUPS, kdegraphics, and possibly other products allows context-dependent attackers to cause a denial of service crash via unknown vectors that trigger an uninitialized pointer...