Clear "self.index_temps" after cleanup to avoid keeping dangling temporary state.

Cython/Compiler/ExprNodes.py

@@ -4376,6 +4376,7 @@ class BufferIndexNode(_IndexingBaseNode):
     def free_temps(self, code):
         for temp in self.index_temps:
             code.funcstate.release_temp(temp)
+        self.index_temps = ()
         super(BufferIndexNode, self).free_temps(code)