added correct insert method for IdManager and SvgElementCollection

Source/SvgElement.cs

@@ -280,7 +280,7 @@ namespace Svg
 
             if (this.OwnerDocument != null)
             {
-                this.OwnerDocument.IdManager.AddAndFixID(this, autoFixID, logElementOldIDNewID);
+                this.OwnerDocument.IdManager.AddAndFixID(this, null, autoFixID, logElementOldIDNewID);
             }
         }
 

Source/SvgElementCollection.cs

@@ -58,7 +58,7 @@ namespace Svg
 
         public void InsertAddAndFixID(int index, SvgElement item, bool autoFixID = true, bool autoFixChildrenID = true, Action<SvgElement, string, string> logElementOldIDNewID = null)
         {
-            AddToIdManager(item, autoFixID, autoFixChildrenID, logElementOldIDNewID);
+            AddToIdManager(item, this._elements[index], autoFixID, autoFixChildrenID, logElementOldIDNewID);
             this._elements.Insert(index, item);
             item._parent.OnElementAdded(item, index);
         }
@@ -86,24 +86,24 @@ namespace Svg
 
         public void AddAndFixID(SvgElement item, bool autoFixID = true, bool autoFixChildrenID = true, Action<SvgElement, string, string> logElementOldIDNewID = null)
         {
-            AddToIdManager(item, autoFixID, autoFixChildrenID, logElementOldIDNewID);
+            AddToIdManager(item, null, autoFixID, autoFixChildrenID, logElementOldIDNewID);
             this._elements.Add(item);
             item._parent.OnElementAdded(item, this.Count - 1);
         }
 
-        private void AddToIdManager(SvgElement item, bool autoFixID = true, bool autoFixChildrenID = true, Action<SvgElement, string, string> logElementOldIDNewID = null)
+        private void AddToIdManager(SvgElement item, SvgElement sibling, bool autoFixID = true, bool autoFixChildrenID = true, Action<SvgElement, string, string> logElementOldIDNewID = null)
         {
             if (!this._mock)
             {
                 if (this._owner.OwnerDocument != null)
                 {
-                    this._owner.OwnerDocument.IdManager.AddAndFixID(item, autoFixID, logElementOldIDNewID);
+                    this._owner.OwnerDocument.IdManager.AddAndFixID(item, sibling, autoFixID, logElementOldIDNewID);
 
                     if (!(item is SvgDocument)) //don't add subtree of a document to parent document
                     {
                         foreach (var child in item.Children)
                         {
-                            child.ApplyRecursive(e => this._owner.OwnerDocument.IdManager.AddAndFixID(e, autoFixChildrenID, logElementOldIDNewID));
+                            child.ApplyRecursive(e => this._owner.OwnerDocument.IdManager.AddAndFixID(e, null, autoFixChildrenID, logElementOldIDNewID));
                         }
                     }
                 }

Source/SvgElementIdManager.cs

@@ -48,7 +48,7 @@ namespace Svg
         /// <param name="element">The <see cref="SvgElement"/> to be managed.</param>
         public virtual void Add(SvgElement element)
         {
-            AddAndFixID(element, false);
+            AddAndFixID(element, null, false);
         }
 
         /// <summary>
@@ -59,7 +59,7 @@ namespace Svg
         /// <param name="autoFixID">Pass true here, if you want the ID to be fixed</param>
         /// <param name="logElementOldIDNewID">If not null, the action is called before the id is fixed</param>
         /// <returns>true, if ID was altered</returns>
-        public virtual bool AddAndFixID(SvgElement element, bool autoFixID = true, Action<SvgElement, string, string> logElementOldIDNewID = null)
+        public virtual bool AddAndFixID(SvgElement element, SvgElement sibling, bool autoFixID = true, Action<SvgElement, string, string> logElementOldIDNewID = null)
         {
             var result = false;
             if (!string.IsNullOrEmpty(element.ID))