Univention Corporate Server 4.2 erratum 620 (extended maintenance)

This update addresses the following issues:
* Buffer over-read in IMA_ADPCM_nibble in audio/SDL_wave.c (CVE-2019-7572)
* Heap-based buffer over-read in InitMS_ADPCM in audio/SDL_wave.c
  (CVE-2019-7573)
* Heap-based buffer over-read in IMA_ADPCM_decode in audio/SDL_wave.c
  (CVE-2019-7574)
* Heap based buffer overflow in function MS_ADPCM_decode in audio/SDL_wave.c
  (CVE-2019-7575)
* Heap-based buffer over-read in InitMS_ADPCM in audio/SDL_wave.c
  (CVE-2019-7576)
* Buffer over-read in function SDL_LoadWAV_RW in audio/SDL_wave.c
  (CVE-2019-7577)
* Heap-based buffer over-read in InitIMA_ADPCM in audio/SDL_wave.c
  (CVE-2019-7578)
* Heap-based buffer over-read in Blit1to4 in video/SDL_blit_1.c
  (CVE-2019-7635)
* Heap-based buffer over-read in SDL_GetRGB in video/SDL_pixels.c
  (CVE-2019-7636)
* Heap-based buffer overflow in SDL_FillRect in video/SDL_surface.c
  (CVE-2019-7637)
* Heap-based buffer over-read in Map1toN in video/SDL_pixels.c
  (CVE-2019-7638)