actually correct add_row_data index handling

stand/aggridx.py

@@ -91,15 +91,22 @@ class aggridx(ui.aggrid):
         # update client
         self.run_grid_method("setGridOption", "columnDefs", new_column_defs)
 
-    def add_row_data(self, rows, index=-1):
+
+    def add_row_data(self, rows, index=None):
         """
         insert rows at the provided index,
         with the default being appending at the bottom of the table
         this operation maintains the current view on the data
         """
+        row_data = self.options["rowData"]
+
         # update server without re-draw
         with self.props.suspend_updates():
-            self.options["rowData"].extend(rows)
+            if index is not None and 0 <= index < len(row_data):
+                row_data[index:index] = rows
+            else:
+                row_data.extend(rows)
+
         # update client
         self.run_grid_method("applyTransaction", {"add": rows, "addIndex": index})