Some configuration may totally miss network interfaces, even localhost. Fixes arduino#4249

Author: Federico Fissore

arduino-core/src/cc/arduino/packages/discoverers/network/NetworkChecker.java

@@ -31,6 +31,8 @@
 
 import javax.jmdns.NetworkTopologyDiscovery;
 import java.net.InetAddress;
+import java.net.NetworkInterface;
+import java.net.SocketException;
 import java.util.*;
 
 public class NetworkChecker extends TimerTask {
@@ -53,6 +55,9 @@ public void start(Timer timer) {
 
   @Override
   public void run() {
+    if (!hasNetworkInterfaces()) {
+      return;
+    }
     try {
       InetAddress[] curentAddresses = topology.getInetAddresses();
       Set<InetAddress> current = new HashSet<>(curentAddresses.length);
@@ -68,4 +73,12 @@ public void run() {
       e.printStackTrace();
     }
   }
+
+  private boolean hasNetworkInterfaces() {
+    try {
+      return NetworkInterface.getNetworkInterfaces() != null;
+    } catch (SocketException e) {
+      return false;
+    }
+  }
 }