Clear old handlers before adding new ones

pettingzoo/sisl/waterworld/waterworld_base.py

@@ -313,6 +313,8 @@ def draw(self):
 
     def add_handlers(self):
         # Collision handlers for pursuers v.s. evaders & poisons
+        self.handlers = []
+
         for pursuer in self.pursuers:
             for obj in self.evaders:
                 self.handlers.append(