fixing the constants thing in theano rnn (keras-team#2429)

Author: braingineer

keras/backend/theano_backend.py

@@ -564,15 +564,15 @@ def rnn(step_function, inputs, initial_states,
     axes = [1, 0] + list(range(2, ndim))
     inputs = inputs.dimshuffle(axes)
 
+    if constants is None:
+        constants = []
+
     if mask is not None:
         if mask.ndim == ndim-1:
             mask = expand_dims(mask)
         assert mask.ndim == ndim
         mask = mask.dimshuffle(axes)
 
-        if constants is None:
-            constants = []
-
         if unroll:
             indices = list(range(input_length))
             if go_backwards:
@@ -641,7 +641,7 @@ def _step(input, mask, output_tm1, *states):
             successive_states = []
             states = initial_states
             for i in indices:
-                output, states = step_function(inputs[i], states)
+                output, states = step_function(inputs[i], states + constants)
                 successive_outputs.append(output)
                 successive_states.append(states)
             outputs = T.stack(*successive_outputs)