Avoid nil pointer panic while assigning private IP on Azure

If any previously assigned IP present in IP configurations
of the NIC is removed from public load balancer backend pool
then cloud-network-config-controller starts to panic due to
a nil pointer.

This PR checks whether load balancer backend pull is nil or
not before proceeding further.

Signed-off-by: Arnab Ghosh <arnabghosh89@gmail.com>

pkg/cloudprovider/azure.go

@@ -143,9 +143,9 @@ func (a *Azure) AssignPrivateIP(ip net.IP, node *corev1.Node) error {
 	// UserDefinedRouting, which doesn't impose such constraints on secondary IPs.
 	loadBalancerBackendAddressPoolsArgument := (*networkInterface.IPConfigurations)[0].LoadBalancerBackendAddressPools
 	var attachedOutboundRule *network.SubResource
-	if (*networkInterface.IPConfigurations)[0].LoadBalancerBackendAddressPools != nil {
-	OuterLoop:
-		for _, ipconfig := range *networkInterface.IPConfigurations {
+OuterLoop:
+	for _, ipconfig := range *networkInterface.IPConfigurations {
+		if ipconfig.LoadBalancerBackendAddressPools != nil {
 			for _, pool := range *ipconfig.LoadBalancerBackendAddressPools {
 				if pool.ID == nil {
 					continue