CLSA-2026-1771857838 freerdp: Fix of 6 CVEs

CVE-2026-23948: fix missing NULL check in core/info - CVE-2026-24491: reset channelcallback before close in drdynvc - CVE-2026-24676: reset audin-format in channels/audin - CVE-2026-24680: reset pointer after memory release in Wayland client - CVE-2026-24681: cancel all USB transfers on channel...