Fix off-by-one error in continuation point calculation.

asyncua/server/history.py

@@ -152,7 +152,7 @@ class HistoryDict(HistoryStorageInterface):
                 results = results[:nb_values]
 
             if len(results) > self.max_history_data_response_size:
-                cont = results[self.max_history_data_response_size + 1].SourceTimestamp
+                cont = results[self.max_history_data_response_size].SourceTimestamp
                 results = results[:self.max_history_data_response_size]
             return results, cont
 
@@ -202,7 +202,7 @@ class HistoryDict(HistoryStorageInterface):
                 results = results[:nb_values]
 
             if len(results) > self.max_history_data_response_size:
-                cont = results[self.max_history_data_response_size + 1].Time
+                cont = results[self.max_history_data_response_size].Time
                 results = results[:self.max_history_data_response_size]
             return results, cont