Univention Corporate Server 4.2 erratum 571 (extended maintenance)

This update addresses the following issues:
* Out of bounds read in sf_write_int (CVE-2018-13139, CVE-2018-19432)
* Global buffer overflow in i2les_array (CVE-2017-8365)
* Heap-based buffer overflow in flac_buffer_copy (CVE-2017-8363)
* Invalid memory read in flac_buffer_copy (CVE-2017-8362)
* Global buffer overflow in flac_buffer_copy (CVE-2017-8361)
* Multiple divide-by-zero issues in double64_init and
  float32_init (CVE-2017-14634) 
* Multiple buffer overflow issues in {d,i}2ulaw_array and
  {d,i}2alaw_array (CVE-2017-17456, CVE-2017-17457, CVE-2018-19662,
  CVE-2018-19661, CVE-2017-14245 and CVE-2017-14246)