Package update exiv2 in branch sisyphus

In Exiv2 0.26, there is an integer overflow leading to a heap-based buffer over-read in the Exiv2::getULong function in types.cpp. Remote attackers can exploit the vulnerability to cause a denial of service via a crafted image file. Note that this vulnerability is different from CVE-2017-14864, which is an invalid memory address dereference.