Fix for duplicate values using setState with initially selected items

see CodeFoxLk#16 (comment)

Author: larakreisz

flutter_multi_select/lib/src/containers/multi_select_container.dart

@@ -119,7 +119,7 @@ class _SimpleMultiSelectContainerState<T>
 
   @override
   void didUpdateWidget(MultiSelectContainer<T> oldWidget) {
-    _addInitiallySelectedItemsToSelectedList();
+    _setPerpetualSelectedItemsCount();
     if (widget.controller != null) {
       widget.controller!.deselectAll = oldWidget.controller!.deselectAll;
       widget.controller!.getSelectedItems =
@@ -140,6 +140,13 @@ class _SimpleMultiSelectContainerState<T>
     setState(() {});
   }
 
+  // find perpetual selected items count
+  void _setPerpetualSelectedItemsCount() {
+    _perpetualSelectedItemsCount =
+        _items.where((item) => item.perpetualSelected).length;
+    setState(() {});
+  }
+
   // Deselect all selected items excluding Perpetual Selected Items
   // for controller deselect call back
   void _deSelectAll() {