Suggested fix for issue #560

[maartenvds]

Summary

Resolves issue (bug) #560
With this fix, the following issue in CVAT will also be resolved and does not need further changes: cvat-ai/cvat#3940

How to test

This was tested manually through the CVAT tool:

1. Create a new project and upload a video
2. Open the task
3. Click Actions -> upload annotations -> MOT 1.1
4. Select zip folder with MOT annotation format (including seqinfo.ini file) and click 'upload'

With this PR, importing should succeed

Checklist

• I submit my changes into the develop branch
• I have added description of my changes into CHANGELOG
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues

[zhiltsov-max]

1. Could you please add a test using seqinfo file in https://github.com/openvinotoolkit/datumaro/blob/develop/tests/test_mot_format.py? Probably, with an example directory in https://github.com/openvinotoolkit/datumaro/tree/develop/tests/assets/mot_dataset.

2. Please add a line in changelog.

[maartenvds]

1. Could you please add a test using seqinfo file in https://github.com/openvinotoolkit/datumaro/blob/develop/tests/test_mot_format.py? Probably, with an example directory in https://github.com/openvinotoolkit/datumaro/tree/develop/tests/assets/mot_dataset.

Done. I added a new assets folder without an img1 directory and with a seqinfo.ini file. I appended a test case in test_mot_format.py that checks if the import works and that all imported fields are as expected. The test fails if I remove my change to mot_format.py.

2. Please add a line in changelog.

Done.

[zhiltsov-max]

Thank you for the contribution!