bandwidth, check: bail out when configuration is missing

Signed-off-by: Miguel Duarte Barroso <mdbarroso@redhat.com>

plugins/meta/bandwidth/main.go

@@ -337,6 +337,9 @@ func cmdCheck(args *skel.CmdArgs) error {
 	}
 
 	bandwidth := getBandwidth(bwConf)
+	if bandwidth == nil {
+		return nil
+	}
 
 	if err = validateSubnets(bandwidth.UnshapedSubnets, bandwidth.ShapedSubnets); err != nil {
 		return fmt.Errorf("failed to check subnets, details %s", err)