fix: Video downloading bug

[PavloNetrebchuk]

• Added filtering of block IDs before download
• Performed minor refactoring

Before	After
https://github.com/openedx/openedx-app-android/assets/71447999/3d381757-ab24-49a5-a108-fcf87a67a416	https://github.com/openedx/openedx-app-android/assets/141041606/de6b02e6-3af1-463e-a01a-aca7b7c9d51a

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