Refs #0. Fix index out of range error in model analysis.

scripts/Muon/GUI/Common/fitting_widgets/basic_fitting/basic_fitting_model.py

@@ -289,7 +289,7 @@ class BasicFittingModel:
         """Clears the undo fit functions and other data for the currently selected index."""
         current_dataset_index = self.fitting_context.current_dataset_index
         for i, dataset_index in reversed(list(enumerate(self.fitting_context.dataset_indices_for_undo))):
-            if dataset_index == current_dataset_index:
+            if dataset_index == current_dataset_index and i < len(self.fitting_context.active_fit_history):
                 del self.fitting_context.active_fit_history[i]
                 del self.fitting_context.dataset_indices_for_undo[i]
                 del self.fitting_context.single_fit_functions_for_undo[i]