i got a bug, at get value

[LiaoRiYang]

if i use CVAT create tfrecord, when i read it will work, but some tfrecord, will got wrong.

tfrecord/tfrecord/reader.py

Line 121 in 5034c32

value = value[0]

then i find sometime it (value) will be a empty list,
so i changed

if len(value)==0:
    value = value
else:
    value = value[0]