Fix TimeSeries parameters resetting across simulations. (#486)

Author: Eric-Vin

src/scenic/core/external_params.py

@@ -381,13 +381,18 @@ def extractOutput(self, value):
 class TimeSeriesParameter:
     def __init__(self, callback):
         self._callback = callback
+        self._lastSimulation = None
         self._lastTime = -1
 
     def getSample(self):
         import scenic.syntax.veneer as veneer
 
         assert veneer.currentSimulation is not None
 
+        if self._lastSimulation is not veneer.currentSimulation:
+            self._lastSimulation = veneer.currentSimulation
+            self._lastTime = -1
+
         if veneer.currentSimulation.currentTime <= self._lastTime:
             raise RuntimeError(
                 "Attempted `getSample` for a TimeSeries external parameter twice in one timestep."