Webm crash

[clsid2]

Sample file

Crashes randomly.

mkv_read_seek() calls avpriv_update_cur_dts() with a null value for stream.

MediaInfo shows a weird first video stream that might be the cause of the issue.

General
Complete name               : C:\test\4dff80e50e7d1525.webm
Format                      : WebM
Format version              : Version 4
File size                   : 5.76 MiB
Duration                    : 1 ms
Overall bit rate mode       : Variable
Overall bit rate            : 48.3 Gb/s
Movie name                  : https://pious.dev
Writing application         : Lavf58.76.100
Writing library             : Lavf58.76.100

Video #1
ID                          : 1
Width                       : 480 pixels
Height                      : 480 pixels
Display aspect ratio        : 1.000

Video #2
ID                          : 2
Format                      : VP9
Codec ID                    : V_VP9
Width                       : 480 pixels
Height                      : 480 pixels
Display aspect ratio        : 1.000
Frame rate mode             : Constant
Frame rate                  : 30.000 FPS
Default                     : No
Forced                      : No

Video #3
ID                          : 3
Format                      : VP9
Codec ID                    : V_VP9
Width                       : 480 pixels
Height                      : 480 pixels
Display aspect ratio        : 1.000
Frame rate mode             : Constant
Frame rate                  : 30.000 FPS
Default                     : No
Forced                      : No

Audio
ID                          : 4
Format                      : Vorbis
Format settings, Floor      : 1
Codec ID                    : A_VORBIS
Duration                    : 1 ms
Bit rate mode               : Variable
Bit rate                    : 64.0 kb/s
Channel(s)                  : 2 channels
Sampling rate               : 48.0 kHz
Compression mode            : Lossy
Stream size                 : 8.00 Bytes (0%)
Writing library             : libVorbis (Reducing Environment) (20200704 (Reducing Environment))
Default                     : Yes
Forced                      : No