Add patch for CVE-2018-5996

Insufficient exception handling in the method NCompress::NRar3::CDecoder::Code
of 7-Zip before 18.00 and p7zip can lead to multiple memory corruptions within
the PPMd code, allows remote attackers to cause a denial of service
(segmentation fault) or execute arbitrary code via a crafted RAR archive.

Obtained from: Debian (link in the patch file)
MFH: 2018Q1
Security: 7a2e0063-0e4e-11e8-94c0-5453ed2e2b49