Fix mseries command with negative step.

src/bundles/model_series/src/mseries.py

@@ -112,7 +112,7 @@ def __init__(self, models, pause_frames = 1, loop = 1, step = 1):
 
   def start(self):
 
-    self.inext = 0 if self.step > 0 else len(models)-1
+    self.inext = 0 if self.step > 0 else len(self.models)-1
     t = self.models[0].session.triggers
     self._handler = t.add_handler('new frame', self.frame_cb)