Fix broken data flow in MultipleChoiceFilter

Author: tom-englert

src/DataGridExtensions/ListBoxSelectAllBehavior.cs

@@ -90,7 +90,10 @@ private void ListBox_CollectionChanged()
 
             if (AreAllFilesSelected.GetValueOrDefault())
             {
-                listBox?.SelectAll();
+                if (listBox?.IsLoaded == true)
+                {
+                    listBox.SelectAll();
+                }
             }
         }
 

src/DataGridExtensions/MultipleChoiceFilter.cs

@@ -245,9 +245,12 @@ private void Filter_Changed()
 
             Text = filter?.Text;
 
-            if (filter?.Items == null && listBox.IsLoaded)
+            if (filter?.Items == null)
             {
-                listBox.SelectAll();
+                if (listBox.IsLoaded)
+                {
+                    listBox.SelectAll();
+                }
                 return;
             }