src: fix a few `Illegal string offset' warnings

src/etc/inc/gwlb.inc

@@ -445,7 +445,7 @@ function return_gateways_array($disabled = false, $localhost = false, $inactive
 
 	$i = -1;
 	/* Process/add all the configured gateways. */
-	if (is_array($config['gateways']['gateway_item'])) {
+	if (isset($config['gateways']['gateway_item'])) {
 		foreach ($config['gateways']['gateway_item'] as $gateway) {
 			/* Increment it here to do not skip items */
 			$i++;
@@ -796,7 +796,7 @@ function return_gateway_groups_array() {
 		fixup_default_gateway("inet", $gateways_status, $gateways_arr);
 		fixup_default_gateway("inet6", $gateways_status, $gateways_arr);
 	}
-	if (is_array($config['gateways']['gateway_group'])) {
+	if (isset($config['gateways']['gateway_group'])) {
 		$carplist = get_configured_carp_interface_list();
 		foreach ($config['gateways']['gateway_group'] as $group) {
 			/* create array with group gateways members separated by tier */

src/etc/inc/interfaces.inc

@@ -185,7 +185,7 @@ function interface_netgraph_needed($interface = "wan") {
 	}
 	if ($found == false) {
 		$realif = get_real_interface($interface);
-		if (is_array($config['ppps']['ppp']) && count($config['ppps']['ppp'])) {
+		if (isset($config['ppps']['ppp'])) {
 			foreach ($config['ppps']['ppp'] as $pppid => $ppp) {
 
 /* This if block doesn't do anything. It can be deleted.

src/etc/inc/system.inc

@@ -387,7 +387,7 @@ function system_routing_configure($interface = '')
 	$interfacegwv6 = "";
 	$foundgwv6 = false;
 	/* tack on all the hard defined gateways as well */
-	if (is_array($config['gateways']['gateway_item'])) {
+	if (isset($config['gateways']['gateway_item'])) {
 		array_map('unlink', glob('/tmp/*_defaultgw{,v6}', GLOB_BRACE));
 		foreach	($config['gateways']['gateway_item'] as $gateway) {
 			if (isset($gateway['defaultgw'])) {