script/check-config.sh: enable set -u, fix issues

One particularly bad one is ${codes[@]} which is fine in bash 4.4+,
but gives "codes[@]: unbound variable" with older bash versions,
such as with bash 4.2 used on CentOS 6. It's good that this is the only
array in the script that can potentially be empty.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

script/check-config.sh

@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-set -e
+set -e -u
 
 # bits of this were adapted from check_config.sh in docker
 # see also https://github.com/docker/docker/blob/master/contrib/check-config.sh
@@ -45,11 +45,11 @@ is_set_as_module() {
 color() {
 	local codes=()
 	if [ "$1" = 'bold' ]; then
-		codes=("${codes[@]}" '1')
+		codes=("${codes[@]-}" '1')
 		shift
 	fi
 	if [ "$#" -gt 0 ]; then
-		local code
+		local code=''
 		case "$1" in
 		# see https://en.wikipedia.org/wiki/ANSI_escape_code#Colors
 		black) code=30 ;;
@@ -62,11 +62,11 @@ color() {
 		white) code=37 ;;
 		esac
 		if [ "$code" ]; then
-			codes=("${codes[@]}" "$code")
+			codes=("${codes[@]-}" "$code")
 		fi
 	fi
 	local IFS=';'
-	echo -en '\033['"${codes[*]}"'m'
+	echo -en '\033['"${codes[*]-}"'m'
 }
 wrap_color() {
 	text="$1"
@@ -134,8 +134,7 @@ is_config() {
 }
 
 search_config() {
-	local target_dir="$1"
-	[[ "$target_dir" ]] || target_dir=("${possibleConfigs[@]}")
+	local target_dir=("${1:-${possibleConfigs[@]}}")
 
 	local tryConfig
 	for tryConfig in "${target_dir[@]}"; do
@@ -159,7 +158,7 @@ search_config() {
 	exit 1
 }
 
-CONFIG="$1"
+CONFIG="${1:-}"
 
 is_config "$CONFIG" || {
 	if [[ ! "$CONFIG" ]]; then