fix: `return 0` instead of `return` if the intent is not to exit build

If the previous if statement checking if PASSES_TO_LAYERS is true,
then the last return code be non-zero and a return statement with no
argument will return the error code of the if statement thus exiting
the script. This is  not our intent. So we need to return 0 here when
layer name as already been registered

debian/changelog

@@ -1,3 +1,10 @@
+livecd-rootfs (24.04.21) noble; urgency=medium
+
+  * Do not exit live image build if PASSES_TO_LAYERS is true and layer
+    is already registered.
+
+ -- Philip Roche <phil.roche@canonical.com>  Wed, 24 Jan 2024 17:59:06 +0000
+
 livecd-rootfs (24.04.20) noble; urgency=medium
 
   * fix: Fix for calling unminimize if lxd-installer package

live-build/auto/config

@@ -109,7 +109,13 @@ _register_pass () {
 
 	case "$PASSES" in
 		*$1*)
-			return
+			# The pass is already registered in the list of layers.
+			# If PASSES_TO_LAYERS is true, then the above if statement's error
+			# code will be non-zero and a return statement with no argument
+			# will return the error code of the if statement, non-zero, thus
+			# exiting the script and build. This is not our intent. So we need
+			# to return 0 here.
+			return 0
 			;;
 	esac