title: crash in ctc loss function
body: <p>I am getting an the following <code>InvalidArgumentError</code> using ctc-loss function in Tensorflow 1.2.0-rc0 (python 2.7):</p>
  
  <pre><code>InvalidArgumentError (see above for traceback): label SparseTensor is not valid: indices[7] = [0,7] is out of bounds: need 0 &lt;= index &lt; [1,7]
           [[Node: loss/CTCLoss = CTCLoss[ctc_merge_repeated=true, ignore_longer_outputs_than_inputs=false, preprocess_collapse_repeated=false, _device="/job:localhost/replica:0/task:0/cpu:0"](output_fc/BiasAdd/_91, _arg_labels/indices_0_1, _arg_labels/values_0_3, seq_len/Cast/_93)]]
           [[Node: loss/CTCLoss/_103 = _Recv[client_terminated=false, recv_device="/job:localhost/replica:0/task:0/gpu:0", send_device="/job:localhost/replica:0/task:0/cpu:0", send_device_incarnation=1, tensor_name="edge_103_loss/CTCLoss", tensor_type=DT_FLOAT, _device="/job:localhost/replica:0/task:0/gpu:0"]()]]
  </code></pre>
  
  <p>I do not understand the:</p>
  
  <pre><code>label SparseTensor is not valid: indices[7] = [0,7] is out of bounds: need 0 &lt;= index &lt; [1,7]
  </code></pre>
  
  <p>Since the <code>SparseTensor</code> (target sequence) that is crashing is (I set a batch size of 1):</p>
  
  <pre><code>(array([[ 0,  0],
         [ 0,  1],
         [ 0,  2],
         [ 0,  3],
         [ 0,  4],
         [ 0,  5],
         [ 0,  6],
         [ 0,  7],
         [ 0,  8],
         [ 0,  9],
         [ 0, 10],
         [ 0, 11],
         [ 0, 12],
         [ 0, 13],
         [ 0, 14],
         [ 0, 15],
         [ 0, 16],
         [ 0, 17],
         [ 0, 18],
         [ 0, 19],
         [ 0, 20],
         [ 0, 21],
         [ 0, 22]], dtype=int32), array([41,  2,  7,  0, 13, 19,  4, 11, 11,  4, 40, 19,  8,  1,  1, 18, 40,
         24,  4,  0,  7, 40, 41], dtype=int32), array([ 1, 23], dtype=int32))
  </code></pre>
  
  <p>In previous iterations it has processed longer sequences with similar values such as:</p>
  
  <pre><code>(array([[  0,   0],
         [  0,   1],
         [  0,   2],
         [  0,   3],
         [  0,   4],
         [  0,   5],
         [  0,   6],
         [  0,   7],
         [  0,   8],
         [  0,   9],
         [  0,  10],
         [  0,  11],
         [  0,  12],
         [  0,  13],
         [  0,  14],
         [  0,  15],
         [  0,  16],
         [  0,  17],
         [  0,  18],
         [  0,  19],
         [  0,  20],
         [  0,  21],
         [  0,  22],
         [  0,  23],
         [  0,  24],
         [  0,  25],
         [  0,  26],
         [  0,  27],
         [  0,  28],
         [  0,  29],
         [  0,  30],
         [  0,  31],
         [  0,  32],
         [  0,  33],
         [  0,  34],
         [  0,  35],
         [  0,  36],
         [  0,  37],
         [  0,  38],
         [  0,  39],
         [  0,  40],
         [  0,  41],
         [  0,  42],
         [  0,  43],
         [  0,  44],
         [  0,  45],
         [  0,  46],
         [  0,  47],
         [  0,  48],
         [  0,  49],
         [  0,  50],
         [  0,  51],
         [  0,  52],
         [  0,  53],
         [  0,  54],
         [  0,  55],
         [  0,  56],
         [  0,  57],
         [  0,  58],
         [  0,  59],
         [  0,  60],
         [  0,  61],
         [  0,  62],
         [  0,  63],
         [  0,  64],
         [  0,  65],
         [  0,  66],
         [  0,  67],
         [  0,  68],
         [  0,  69],
         [  0,  70],
         [  0,  71],
         [  0,  72],
         [  0,  73],
         [  0,  74],
         [  0,  75],
         [  0,  76],
         [  0,  77],
         [  0,  78],
         [  0,  79],
         [  0,  80],
         [  0,  81],
         [  0,  82],
         [  0,  83],
         [  0,  84],
         [  0,  85],
         [  0,  86],
         [  0,  87],
         [  0,  88],
         [  0,  89],
         [  0,  90],
         [  0,  91],
         [  0,  92],
         [  0,  93],
         [  0,  94],
         [  0,  95],
         [  0,  96],
         [  0,  97],
         [  0,  98],
         [  0,  99],
         [  0, 100],
         [  0, 101],
         [  0, 102],
         [  0, 103],
         [  0, 104],
         [  0, 105],
         [  0, 106],
         [  0, 107],
         [  0, 108],
         [  0, 109],
         [  0, 110]], dtype=int32), array([41, 22,  4, 36, 17,  4, 40,  6, 14,  8, 13,  6, 40, 19, 14, 40,  4,
          0, 19, 40,  8, 19, 40, 22,  4, 36, 17,  4, 40,  6, 14,  8, 13,  6,
         40, 19, 14, 40, 14, 15,  4, 13, 40, 20, 15, 40, 18, 14, 12,  4, 40,
         22,  8, 13,  4, 40,  0, 13,  3, 40, 22,  4, 36, 17,  4, 40,  6, 14,
          8, 13,  6, 40, 19, 14, 40, 19,  4, 11, 11, 40, 24, 14, 20, 40, 18,
         19, 14, 17,  0,  6,  4, 40,  7, 14, 22, 40, 12, 20,  2,  7, 40,  8,
         19, 40,  2, 14, 18, 19, 18, 40, 41], dtype=int32), array([  1, 111], dtype=int32))
  </code></pre>
  
  <p>Thank you in advance.</p>