abort if configuration is not readable

bin/access-check-manager.cgi.in

@@ -12,6 +12,9 @@ use AccountManager::App;
 my $configuration_file =
     $ENV{ACCOUNTMANAGER_CONFIG} || '@confdir@/manager.conf';
 my $configuration = Config::Tiny->read($configuration_file);
+if (!$configuration) {
+    die Config::Tiny->errstr() . "\n";
+}
 
 my $app = AccountManager::App->new(
     configuration => $configuration