Univention Corporate Server 4.2 erratum 523 (extended maintenance)

This update addresses the following issues:
* heap-based buffer over-read in the ParseImageResourceBlocks function in
  coders/psd.c (CVE-2018-16412)
* heap-based buffer over-read in the PushShortPixel function in
  MagickCore/quantum-private.h (CVE-2018-16413)
* out-of-bounds write in InsertRow function in coders/cut.c (CVE-2018-16642)
* missing check for fputc function in multiple files (CVE-2018-16643)
* improper check for length in ReadDCMImage of coders/dcm.c and ReadPICTImage
  of coders/pict.c (CVE-2018-16644)
* Out-of-memory ReadBMPImage of coders/bmp.c and ReadDIBImage of codes/dib.c
  (CVE-2018-16645)
* Missing NULL check in ReadOneJNGImage in coders/png.c (CVE-2018-16749)