Keep things from being dropped off the map

EduNetworkBuilder/NetworkDevice.cs

@@ -821,16 +821,32 @@ namespace EduNetworkBuilder
         {
             return new Rectangle(MyLocation.X, MyLocation.Y, Size, Size);
 
+        }
+
+        private void TryPutLocation(Point Location)
+        {
+            Network myNet = NB.GetNetwork();
+            if (myNet == null) {
+                MyLocation = Location; // We cannot do checking.  Hope for the best.
+                return;
+            }
+            int x = Location.X;
+            int y = Location.Y;
+            if (x < 0) x = 0;
+            if (x > myNet.myWidth - Size) x = myNet.myWidth - Size;
+            if (y < 0) y = 0;
+            if (y > myNet.myHeight - Size) y = myNet.myHeight - Size;
+            MyLocation = new Point(x,y);
+            IsDirty = true;
+
         }
         public void ChangeLocation(Point Location)
         {
-            MyLocation = NB.GetSnapped(Location);
+            TryPutLocation(NB.GetSnapped(Location));
-            IsDirty = true;
         }
         public void ChangeLocationUnsnapped(Point Location)
         {
-            MyLocation = Location;
+            TryPutLocation(Location);
-            IsDirty = true;
         }
 
         public void SetSize(int tSize)