Merge pull request kaldi-asr#1000 from danpovey/online_decoder_fix

Fix for online-decoder crash reported in PR kaldi-asr#993 by @fanskyer

src/nnet2/nnet-compute-online.cc

@@ -42,6 +42,12 @@ void NnetOnlineComputer::Compute(const CuMatrixBase<BaseFloat> &input,
   if (input.NumRows() == 0) {
     output->Resize(0, 0);
     return;
+  } else {
+    // store the last frame as it might be needed for padding when Flush() is
+    // called.
+    if (last_seen_input_frame_.Dim() != input.NumCols())
+      last_seen_input_frame_.Resize(input.NumCols());
+    last_seen_input_frame_.CopyFromVec(input.Row(input.NumRows() - 1));
   }
 
   // Checking if feature dimension matches that required by the neural network.
@@ -100,8 +106,6 @@ void NnetOnlineComputer::Compute(const CuMatrixBase<BaseFloat> &input,
       nnet_.LeftContext() + nnet_.RightContext() + 1) {
     // we have sufficient frames to compute at least one nnet output
     nnet_.ComputeChunkInfo(num_effective_input_rows, 1, &chunk_info_);
-    // store the last frame as it might be needed for padding
-    last_seen_input_frame_ = input_data.Row(input_data.NumRows() - 1);
     Propagate();
     *output = data_.back();
   } else {
@@ -110,6 +114,7 @@ void NnetOnlineComputer::Compute(const CuMatrixBase<BaseFloat> &input,
     // not enough input context so just return an empty array
     output->Resize(0, 0);
   }
+
 }
 
 void NnetOnlineComputer::Flush(CuMatrix<BaseFloat> *output) {
@@ -182,7 +187,7 @@ void NnetOnlineComputer::Propagate() {
     // Hence we manipulate the chunk_info objects to reflect the state of the
     // actual chunk, each component is computing, in the current Propagate.
     // As before we always assume the chunks are contiguous.
-    
+
     // modifying the input chunk_info
     int32 chunk_size_assumed = chunk_info_[c].ChunkSize();
     int32 last_offset = chunk_info_[c].GetOffset(chunk_size_assumed - 1);
@@ -194,7 +199,7 @@ void NnetOnlineComputer::Propagate() {
     // modifying the output chunk_info
     chunk_size_assumed = chunk_info_[c + 1].ChunkSize();
     last_offset = chunk_info_[c + 1].GetOffset(chunk_size_assumed - 1);
-    first_offset = last_offset - (input_data.NumRows() - 
+    first_offset = last_offset - (input_data.NumRows() -
                                   (component.Context().back() -
                                    component.Context().front())) + 1;
     ChunkInfo output_chunk_info(chunk_info_[c + 1].NumCols(),