backup: Ignore any empty lines in backup include list

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>

config/backup/backup.pl

@@ -36,8 +36,10 @@ list_addons() {
 
 process_includes() {
 	local include
-
 	for include in $@; do
+		# Skip any empty line (which will include /)
+		[ -n "${include}" ] || continue
+
 		local file
 		while read -r file; do
 			for file in /${file}; do