fix: crash current must not be NaN during bulk download

[dixidroid]

Description

LEARNER-10248

Fix crash of IllegalArgumentException - current must not be NaN during bulk download.

• Add validation to ensure that the progress value is not NaN.

Steps to reproduce (specific courses)

Variant-1

• Open the course named Quantum Mechanics for Scientists and Engineers 1
• Click on the video tab and start that bulk download.
• Try to expand the sections from the video tab, that lead the app to the crash.

Variant-2

• Open the course named Quantum Mechanics for Scientists and Engineers 1
• Click on the video tab and start that bulk download.
• Rapidly click on the arrow icon to expand the section from the Home tab, and the action leads the app to the crash.

[openedx-webhooks]

Thanks for the pull request, @dixidroid!

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