libX11: Fix of 6 CVEs

CVE-2018-14599: fix off-by-one writes in XListExtensions, XGetFontPath and XListFonts - CVE-2018-14600: fix out-of-bounds write in XListExtensions and XGetFontPath - CVE-2018-14598: fix crash on invalid reply in XListExtensions and XGetFontPath - CVE-2021-31535: reject strings longer than...