Univention Corporate Server 4.4 erratum 650 (security)

This update addresses the following issues:
* heap-based buffer overflow at MagickCore/statistic.c in EvaluateImages
  because of mishandling columns (CVE-2019-13300)
* stack-based buffer overflow at coders/pnm.c in WritePNMImage because of a
  misplaced assignment (CVE-2019-13304)
* stack-based buffer overflow at coders/pnm.c in WritePNMImage because of
  off-by-one errors (CVE-2019-13306)
* heap-based buffer overflow at MagickCore/statistic.c in EvaluateImages
  because of mishandling rows (CVE-2019-13307)
* Use after free in ReadMATImage in coders/mat.c (CVE-2019-15140)
* heap-based buffer overflow in WriteSGIImage in coders/sgi.c
  (CVE-2019-19948)