p7zip -- Null pointer dereference

MITRE reports:

A null pointer dereference bug affects the 16.02 and many old
versions of p7zip. A lack of null pointer check for the variable
folders.PackPositions in function
CInArchive::ReadAndDecodePackedStreams, as used in
the 7z.so library and in 7z applications, will cause a crash and a
denial of service when decoding malformed 7z files.