CLSA-2026-1789668422 libxml2: Fix of 5 CVEs

CVE-2026-86140: add bounds checks around the parenthesis writes in xmlSnprintfElements - CVE-2026-86141: check the xmlStrdup result in xmlRegNewParserCtxt so a failed allocation cannot leave a NULL parser cursor - CVE-2026-86142: make xmlStrlen saturate above INTMAX and reject the saturated...