Fixed statistics modal when the job is assigned to someone

[bsekachev]

Motivation and context

Resolved #4140

How has this been tested?

Manual testing

Checklist

• I submit my changes into the develop branch
• I have added a description of my changes into CHANGELOG file
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues (read github docs)
• I have increased versions of npm packages if it is necessary (cvat-canvas,
  cvat-core, cvat-data and cvat-ui)

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.
• I have updated the license header for each file (see an example below)

# Copyright (C) 2021 Intel Corporation
#
# SPDX-License-Identifier: MIT

[bsekachev]

@dvkruchinin Could you please cover this check in one of existing tests?

[dvkruchinin]

@bsekachev

Could you please cover this check in one of existing tests?

Sure. I`ll update a test.