Fixing issue when DataGrid are nested (#2902)

Fixes #2852

Author: Keboo

MaterialDesignThemes.Wpf/DataGridAssist.cs

@@ -244,6 +244,15 @@ private static void AllowDirectEditWithoutFocus(object sender, MouseButtonEventA
                 // If the cell is already being edited, we don't want to (re)start editing
                 return;
             }
+            //NB: Issue 2852 - Don't handle events from nested data grids
+            var parentDataGrid = dataGridCell
+                .GetVisualAncestry()
+                .OfType<DataGrid>()
+                .FirstOrDefault();
+            if (parentDataGrid != dataGrid)
+            {
+                return;
+            }
 
             dataGrid.CurrentCell = new DataGridCellInfo(dataGridCell);
             dataGrid.BeginEdit();