fix using disconnected as mem buffer

theano/scan_module/scan_op.py

@@ -1624,7 +1624,11 @@ class Scan(PureOp):
         n_mitmot_inps = 0
 
         for idx in xrange(self.n_mit_mot):
-            outer_inp_mitmot.append(dC_douts[idx][::-1])
+            if isinstance(dC_douts[idx].type, DisconnectedType):
+                out = outs[idx]
+                outer_inp_mitmot.append(tensor.zeros_like(out))
+            else:
+                outer_inp_mitmot.append(dC_douts[idx][::-1])
             mitmot_inp_taps.append([])
             mitmot_out_taps.append([])
             undefined = False