nnet1: bugfix in MultiTaskLoss,

- in case a task gets 0 frames, use 0.0 as objective value, avoid nan,

src/nnet/nnet-loss.cc

@@ -163,8 +163,9 @@ void Xent::Eval(const VectorBase<BaseFloat> &frame_weights,
 std::string Xent::Report() {
   std::ostringstream oss;
   oss << "AvgLoss: " << (loss_-entropy_)/frames_ << " (Xent), "
-      << "[AvgXent: " << loss_/frames_ 
-      << ", AvgTargetEnt: " << entropy_/frames_ << "]" << std::endl;
+      << "[AvgXent " << loss_/frames_ 
+      << ", AvgTargetEnt " << entropy_/frames_ 
+      << ", frames " << frames_ << "]" << std::endl;
   if (loss_vec_.size() > 0) {
      oss << "progress: [";
      std::copy(loss_vec_.begin(),loss_vec_.end(),std::ostream_iterator<float>(oss," "));
@@ -257,7 +258,8 @@ std::string Mse::Report() {
   BaseFloat root_mean_square = sqrt(loss_/frames_/num_tgt);
   // build the message,
   std::ostringstream oss;
-  oss << "AvgLoss: " << loss_/frames_ << " (Mse), " << "[RMS " << root_mean_square << "]" << std::endl;
+  oss << "AvgLoss: " << loss_/frames_ << " (Mse), " 
+      << "[RMS " << root_mean_square << ", frames " << frames_ << "]" << std::endl;
   oss << "progress: [";
   std::copy(loss_vec_.begin(),loss_vec_.end(),std::ostream_iterator<float>(oss," "));
   oss << "]" << std::endl;
@@ -372,7 +374,12 @@ std::string MultiTaskLoss::Report() {
 BaseFloat MultiTaskLoss::AvgLoss() {
   BaseFloat ans(0.0);
   for (int32 i = 0; i < loss_vec_.size(); i++) {
-    ans += loss_weights_[i] * loss_vec_[i]->AvgLoss();
+    BaseFloat val = loss_weights_[i] * loss_vec_[i]->AvgLoss();
+    if(!KALDI_ISFINITE(val)) {
+      KALDI_WARN << "Loss " << i+1 << ", has bad objective function value '" << val << "', using 0.0 instead.";
+      val = 0.0;
+    }
+    ans += val;
   }
   return ans;
 }