Make config_item() more robust

debian/changelog

+grub2 (2.06-9) UNRELEASED; urgency=medium
+
+  [ Steve McIntyre ]
+  * postinst: make config_item() more robust
+
+ -- Steve McIntyre <93sam@debian.org>  Thu, 23 Feb 2023 22:30:32 +0000
+
 grub2 (2.06-8.1) experimental; urgency=medium
 
   * Non-maintainer upload.

debian/postinst.in

@@ -301,7 +301,9 @@ config_item()
 {
   for x in /etc/default/grub /etc/default/grub.d/*.cfg; do
     if [ -e "$x" ]; then
-      . "$x"
+	# Lose any output here so we don't confuse our
+	# caller. The xen packages echo stuff here, Aargh!
+      . "$x" > /dev/null
     fi
   done
   if [ "$(eval echo "\${$1+set}")" = set ]; then