decord._ffi.base.DECORDError from VideoReader

Hi, there seems to be some problem with videos containing corrupted frames.

Video, script, and logs available at [Google drive](https://drive.google.com/drive/folders/1dlNSZwHWzxNQVs5MCp2hpoLerHwo4ZX1?usp=sharing).

Video is from the [MEVA](http://mevadata.org) dataset. It is loadable by `cv2.VideoCapture`, `pymovie.editor.VideoFileClip`, and `avi_r.AVIReader` but contains several corrupted frames as detailed [here](https://github.com/CMU-INF-DIVA/avi-r/blob/master/docs/speed.md).

Environment: Mac OS 10.15.5, python 3.7, decord 0.4.0; also reproducible on Linux.
```raw
# Name Version Build Channel
ca-certificates 2020.6.24 0
certifi 2020.6.20 py37_0
decord 0.4.0 pypi_0 pypi
libcxx 10.0.0 1
libedit 3.1.20191231 h1de35cc_1
libffi 3.3 hb1e8313_2
ncurses 6.2 h0a44026_1
numpy 1.19.0 pypi_0 pypi
openssl 1.1.1g h1de35cc_0
pip 20.1.1 py37_1
python 3.7.7 hf48f09d_4
readline 8.0 h1de35cc_0
setuptools 49.2.0 py37_0
sqlite 3.32.3 hffcf06c_0
tk 8.6.10 hb0a8c7a_0
wheel 0.34.2 py37_0
xz 5.2.5 h1de35cc_0
zlib 1.2.11 h1de35cc_3
```

Script:
```python
from decord import VideoReader
from decord import cpu

vr = VideoReader('2018-03-07.16-55-06.17-00-06.school.G336.avi', ctx=cpu(0))
for i in range(len(vr)):
frame = vr[i]
print(i, frame.shape)
```

Log:
```raw
[NULL @ 0x7fde3829b200] missing picture in access unit with size 56
[NULL @ 0x7fde3829b200] missing picture in access unit with size 56
[NULL @ 0x7fde3829b200] missing picture in access unit with size 56
[NULL @ 0x7fde3829b200] missing picture in access unit with size 56
[NULL @ 0x7fde3829b200] missing picture in access unit with size 56
[NULL @ 0x7fde3829b200] missing picture in access unit with size 56
Invalid UE golomb code
[NULL @ 0x7fde3829b200] pps_id 3199971767 out of range
[NULL @ 0x7fde3829b200] sps_id 3 out of range
[NULL @ 0x7fde3829b200] missing picture in access unit with size 56
[NULL @ 0x7fde3829b200] sps_id 3 out of range
[NULL @ 0x7fde3829b200] SEI type 0 size 568 truncated at 256
[NULL @ 0x7fde3829b200] non-existing PPS 176 referenced
[NULL @ 0x7fde3829b200] SEI type 0 size 568 truncated at 256
[NULL @ 0x7fde3829b200] non-existing PPS 176 referenced
Invalid UE golomb code
[NULL @ 0x7fde3829b200] pps_id 3199971767 out of range
[NULL @ 0x7fde3829b200] sps_id 32 out of range
[NULL @ 0x7fde3829b200] missing picture in access unit with size 56
[NULL @ 0x7fde3829b200] missing picture in access unit with size 56
[NULL @ 0x7fde3829b200] missing picture in access unit with size 56
[NULL @ 0x7fde3829b200] missing picture in access unit with size 56
[NULL @ 0x7fde3829b200] missing picture in access unit with size 56
[NULL @ 0x7fde3829b200] missing picture in access unit with size 56
Invalid UE golomb code
[NULL @ 0x7fde3829b200] pps_id 3199971767 out of range
[NULL @ 0x7fde3829b200] sps_id 3 out of range
[NULL @ 0x7fde3829b200] missing picture in access unit with size 56
[NULL @ 0x7fde3829b200] sps_id 3 out of range
[NULL @ 0x7fde3829b200] SEI type 0 size 568 truncated at 256
[NULL @ 0x7fde3829b200] non-existing PPS 176 referenced
[NULL @ 0x7fde3829b200] SEI type 0 size 568 truncated at 256
[NULL @ 0x7fde3829b200] non-existing PPS 176 referenced
Invalid UE golomb code
[NULL @ 0x7fde3829b200] pps_id 3199971767 out of range
[NULL @ 0x7fde3829b200] sps_id 32 out of range
[h264 @ 0x7fde1800b400] No start code is found.
[h264 @ 0x7fde1800b400] Error splitting the input into NAL units.
[h264 @ 0x7fde18048400] No start code is found.
[h264 @ 0x7fde18048400] Error splitting the input into NAL units.
[h264 @ 0x7fde18048a00] No start code is found.
[h264 @ 0x7fde18048a00] Error splitting the input into NAL units.
[h264 @ 0x7fde1808c200] No start code is found.
[h264 @ 0x7fde1808c200] Error splitting the input into NAL units.
[h264 @ 0x7fde1808c800] No start code is found.
[h264 @ 0x7fde1808c800] Error splitting the input into NAL units.
[h264 @ 0x7fde18016600] No start code is found.
[h264 @ 0x7fde18016600] Error splitting the input into NAL units.
0 (1080, 1920, 3)
... (Omitted)
103 (1080, 1920, 3)
Traceback (most recent call last):
File "test.py", line 6, in
frame = vr[i]
File "/Users/lijun/Applications/miniconda3/envs/decord/lib/python3.7/site-packages/decord/video_reader.py", line 92, in __getitem__
return self.next()
File "/Users/lijun/Applications/miniconda3/envs/decord/lib/python3.7/site-packages/decord/video_reader.py", line 104, in next
arr = _CAPI_VideoReaderNextFrame(self._handle)
File "/Users/lijun/Applications/miniconda3/envs/decord/lib/python3.7/site-packages/decord/_ffi/_ctypes/function.py", line 175, in __call__
ctypes.byref(ret_val), ctypes.byref(ret_tcode)))
File "/Users/lijun/Applications/miniconda3/envs/decord/lib/python3.7/site-packages/decord/_ffi/base.py", line 63, in check_call
raise DECORDError(py_str(_LIB.DECORDGetLastError()))
decord._ffi.base.DECORDError: [16:53:10] /Users/travis/build/zhreshold/decord-distro/decord/src/video/ffmpeg/threaded_decoder.cc:288: [16:53:10] /Users/travis/build/zhreshold/decord-distro/decord/src/video/ffmpeg/threaded_decoder.cc:216: Check failed: avcodec_send_packet(dec_ctx_.get(), pkt.get()) >= 0 (-1094995529 vs. 0) Thread worker: Error sending packet.

Stack trace returned 7 entries:
[bt] (0) 0 libdecord.dylib 0x0000000112db2d70 dmlc::StackTrace(unsigned long) + 464
[bt] (1) 1 libdecord.dylib 0x0000000112db2a54 dmlc::LogMessageFatal::~LogMessageFatal() + 52
[bt] (2) 2 libdecord.dylib 0x0000000112df2b16 decord::ffmpeg::FFMPEGThreadedDecoder::WorkerThreadImpl() + 390
[bt] (3) 3 libdecord.dylib 0x0000000112df0d29 decord::ffmpeg::FFMPEGThreadedDecoder::WorkerThread() + 25
[bt] (4) 4 libdecord.dylib 0x0000000112df41ee void* std::__1::__thread_proxy >, void (decord::ffmpeg::FFMPEGThreadedDecoder::*)(), decord::ffmpeg::FFMPEGThreadedDecoder*> >(void*) + 62
[bt] (5) 5 libsystem_pthread.dylib 0x00007fff72534109 _pthread_start + 148
[bt] (6) 6 libsystem_pthread.dylib 0x00007fff7252fb8b thread_start + 15

Stack trace returned 10 entries:
[bt] (0) 0 libdecord.dylib 0x0000000112db2d70 dmlc::StackTrace(unsigned long) + 464
[bt] (1) 1 libdecord.dylib 0x0000000112db2a54 dmlc::LogMessageFatal::~LogMessageFatal() + 52
[bt] (2) 2 libdecord.dylib 0x0000000112df0cae decord::ffmpeg::FFMPEGThreadedDecoder::CheckErrorStatus() + 142
[bt] (3) 3 libdecord.dylib 0x0000000112df171a decord::ffmpeg::FFMPEGThreadedDecoder::Pop(decord::runtime::NDArray*) + 58
[bt] (4) 4 libdecord.dylib 0x0000000112de812c decord::VideoReader::NextFrameImpl() + 108
[bt] (5) 5 libdecord.dylib 0x0000000112de8318 decord::VideoReader::NextFrame() + 24
[bt] (6) 6 libdecord.dylib 0x0000000112ddcb9d std::__1::__function::__func, void (decord::runtime::DECORDArgs, decord::runtime::DECORDRetValue*)>::operator()(decord::runtime::DECORDArgs&&, decord::runtime::DECORDRetValue*&&) + 77
[bt] (7) 7 libdecord.dylib 0x0000000112daf5b6 DECORDFuncCall + 70
[bt] (8) 8 libffi.7.dylib 0x000000010226bead ffi_call_unix64 + 85
[bt] (9) 9 ??? 0x00007ffeede011b0 0x0 + 140732889305520
```