Security update for libxml2 (moderate)

This update for libxml2 fixes the following security issues:

• CVE-2018-9251: The xz_decomp function allowed remote attackers to cause
  a denial of service (infinite loop) via a crafted XML file that triggers
  LZMA_MEMLIMIT_ERROR, as demonstrated by xmllint (bsc#1088279).
• CVE-2018-14567: Prevent denial of service (infinite loop) via a crafted
  XML file that triggers LZMA_MEMLIMIT_ERROR, as demonstrated by xmllint
  (bsc#1105166).
• CVE-2018-14404: Prevent NULL pointer dereference in the
  xmlXPathCompOpEval() function when parsing an invalid XPath expression
  in the XPATH_OP_AND or XPATH_OP_OR case leading to a denial of service
  attack (bsc#1102046).
• CVE-2017-18258: The xz_head function allowed remote attackers to cause a
  denial of service (memory consumption) via a crafted LZMA file, because
  the decoder functionality did not restrict memory usage to what is
  required for a legitimate file (bsc#1088601).

This update was imported from the SUSE:SLE-12-SP2:Update update project.