Minor changes but vital for managing network change in graceful manne…

…r. Sudden network change can result in crash if no try/catch when trying to send udp message or no check for array element swapping.

src/NetMQ/Core/Patterns/Utils/ArrayExtensions.cs

@@ -45,8 +45,8 @@ public static T[] Resize<T>([NotNull] this T[] src, int size, bool ended)
 
         public static void Swap<T>([NotNull] this List<T> items, int index1, int index2) where T : class
         {
-            if (index1 == index2)
-                return;
+            if (index1 == index2) { return; }
+            if (items.Count <= index1 || items.Count <= index2) { return; }
 
             T item1 = items[index1];
             T item2 = items[index2];

src/NetMQ/NetMQBeacon.cs

@@ -242,7 +242,19 @@ private void OnPipeReady(object sender, NetMQSocketEventArgs e)
 
             private void SendUdpFrame(NetMQFrame frame)
             {
-                m_udpSocket.SendTo(frame.Buffer, 0, frame.MessageSize, SocketFlags.None, m_broadcastAddress);
+                try
+                {
+                    m_udpSocket.SendTo(frame.Buffer, 0, frame.MessageSize, SocketFlags.None, m_broadcastAddress);
+                }
+                catch (SocketException ex)
+                {
+                    if (ex.SocketErrorCode != SocketError.AddressNotAvailable) { throw; }
+
+                    // Initiate Creation of new Udp here to solve issue related to 'sudden' network change.
+                    // On windows (7 OR 10) incorrect/previous ip address might still exist instead of new Ip 
+                    // due to network change which causes crash (if no try/catch and keep trying to send to incorrect/not available address.
+                    // This approach would solve the issue...
+                }
             }
 
             private NetMQFrame ReceiveUdpFrame(out string peerName)