fix: unset SUDO_USER before armbian-config chroot call

Host's SUDO_USER=igorp leaks into the chroot via chroot_sdcard.
module_desktop_getuser tries `id $SUDO_USER` which fails with
'id: igorp: no such user' because the host user doesn't exist in
the chroot's /etc/passwd. Clear it so getuser falls through to
the awk path (and mode=build skips the call entirely once
configng PR #859 is published to apt.armbian.com).

Author: igorpecovnik

lib/functions/rootfs/distro-agnostic.sh

@@ -424,7 +424,13 @@ function install_distribution_agnostic() {
 		# start/autologin) — no real user exists at image-build time;
 		# armbian-firstrun creates the first user on first boot.
 		# See armbian/configng#859.
-		chroot_sdcard "DEBIAN_FRONTEND=noninteractive armbian-config --api module_desktops install de=${DESKTOP_ENVIRONMENT} tier=${DESKTOP_TIER:-mid} mode=build"
+		# SUDO_USER= unset: host's SUDO_USER leaks into the chroot
+		# via chroot_sdcard. module_desktop_getuser tries `id $SUDO_USER`
+		# which fails noisily because the host user doesn't exist in the
+		# chroot's /etc/passwd. Clearing it lets getuser fall through to
+		# the awk path (which finds nothing in build mode → mode=build
+		# skips it entirely).
+		chroot_sdcard "SUDO_USER= DEBIAN_FRONTEND=noninteractive armbian-config --api module_desktops install de=${DESKTOP_ENVIRONMENT} tier=${DESKTOP_TIER:-mid} mode=build"
 
 		# Disable display managers for first boot — armbian-firstrun
 		# enables the appropriate one after initial setup completes.