Add default values to PASS in canary hooks.

debian/changelog

@@ -1,3 +1,10 @@
+livecd-rootfs (2.824) UNRELEASED; urgency=medium
+
+  * Fix build failures of desktop raspi images due to canary hooks
+    interfering.
+
+ -- Łukasz 'sil2100' Zemczak <lukasz.zemczak@ubuntu.com>  Thu, 13 Apr 2023 09:43:58 +0200
+
 livecd-rootfs (2.823) lunar; urgency=medium
 
   * Update infinite_scream URL to mastodon

live-build/ubuntu/hooks/020-canary-enhanced-sb.binary

@@ -2,7 +2,7 @@
 
 set -eux
 
-case $PASS in
+case ${PASS:-} in
     minimal.standard.enhanced-secureboot)
         ;;
     *)

live-build/ubuntu/hooks/020-canary-live.binary

@@ -2,7 +2,7 @@
 
 set -eux
 
-case $PASS in
+case ${PASS:-} in
     minimal.standard.live)
         ;;
     *)

live-build/ubuntu/hooks/020-canary-live.chroot_early

@@ -2,7 +2,7 @@
 
 set -eu
 
-case $PASS in
+case ${PASS:-} in
     minimal.standard.live)
         ;;
     *)