Updated exempi package fixes security vulnerabilities

An issue was discovered in Exempi through 2.4.4. There is a stack-based buffer over-read in the PostScript_MetaHandler::ParsePSFile() function in PostScript_Handler.cpp (CVE-2018-7729). An issue was discovered in Exempi through 2.4.4. WEBP_Support.cpp does not check whether a bitstream has a NULL value, leading to a NULL pointer dereference in the WEBP::VP8XChunk class (CVE-2018-7731). An issue was discovered in Exempi before 2.4.4. Integer overflow in the Chunk class in RIFF.cpp allows remote attackers to cause a denial of service (infinite loop) via crafted XMP data in a .avi file (CVE-2017-18233). An issue was discovered in Exempi before 2.4.3. It allows remote attackers to cause a denial of service (invalid memcpy with resultant use-after-free) or possibly have unspecified other impact via a .pdf file containing JPEG data, related to ReconcileTIFF.cpp, TIFF_MemoryReader.cpp, and TIFF_Support.hpp (CVE-2017-18234). An issue was discovered in Exempi before 2.4.3. The VPXChunk class in WEBP_Support.cpp does not ensure nonzero widths and heights, which allows remote attackers to cause a denial of service (assertion failure and application exit) via a crafted .webp file (CVE-2017-18235). An issue was discovered in Exempi before 2.4.4. The ASF_Support::ReadHeaderObject function in ASF_Support.cpp allows remote attackers to cause a denial of service (infinite loop) via a crafted .asf file (CVE-2017-18236). An issue was discovered in Exempi before 2.4.3. The PostScript_Support::ConvertToDate function in PostScript_Support.cpp allows remote attackers to cause a denial of service (invalid pointer dereference and application crash) via a crafted .ps file (CVE-2017-18237).