[scripts] small fix for utils/dict_dir_add_pronprobs.sh (#1912)

Author: wantee

egs/wsj/s5/utils/dict_dir_add_pronprobs.sh

@@ -50,6 +50,7 @@ fi
 
 if [ ! -s $pron_counts ]; then
  echo "$0: expected file $pron_counts to exist";
+ exit 1;
 fi
 
 mkdir -p $dir || exit 1;