Fix off-by-one error

Author: andystaples

azure/durable_functions/models/TaskOrchestrationExecutor.py

@@ -95,7 +95,7 @@ def execute(self, context: DurableOrchestrationContext,
         # Combine the is_played field with the history-based signal:
         # we are replaying if is_played says so OR if we haven't reached new events yet.
         execution_started_event = history[1]
-        history_is_replaying = self._new_events_start_index > 1
+        history_is_replaying = self._new_events_start_index >= 0
         self.current_task.is_played = execution_started_event.is_played or history_is_replaying
 
         # If user code is a generator, then it uses `yield` statements (the DF API)
@@ -294,7 +294,7 @@ def _find_new_events_start_index(self, history: List[HistoryEvent]) -> int:
             The index of the last OrchestratorStarted event, which is the
             boundary between old (replayed) and new events.
         """
-        last_orchestrator_started_index = 0
+        last_orchestrator_started_index = -1
         for i, event in enumerate(history):
             if event.event_type == HistoryEventType.ORCHESTRATOR_STARTED:
                 last_orchestrator_started_index = i