Fix sequence bounds check for parent tasks.

cylc/flow/taskdef.py

@@ -140,7 +140,7 @@ def get_parent_points(self, point):
         """Return the cycle points of my parents, at point."""
         parent_points = set()
         for seq in self.sequences:
-            if not seq.is_on_sequence(point):
+            if not seq.is_valid(point):
                 continue
             if seq in self.dependencies:
                 # task has prereqs in this sequence
@@ -155,7 +155,7 @@ def get_abs_triggers(self, point):
         """Return my absolute triggers, if any, at point."""
         abs_triggers = set()
         for seq in self.sequences:
-            if not seq.is_on_sequence(point):
+            if not seq.is_valid(point):
                 continue
             if seq in self.dependencies:
                 # task has prereqs in this sequence