add an activity check for the permission check

[Donutcheese]

Description (required)

Fixes #INSERT_ISSUE_NUMBER_HERE

What changes did you make and why?
Added SecurityException Handling:

Wrapped the creation of DownloadManager.Request in a try-catch block to handle SecurityException if storage permission is missing. This prevents the app from crashing when permissions are revoked during download.
Checked for Non-null activity Before Enqueuing:

Added a null check for activity before calling enqueueRequest. This ensures the activity is still valid, especially when permissions are revoked or the activity is recreated.
Enhanced Documentation:

Added detailed doc comments for the class and each method, explaining the purpose and functionality of the code, making it more readable and maintainable.

Tests performed (required)

Tested {build variant, e.g. ProdDebug} on {name of device or emulator} with API level {API level}.
ProdDebug on samsung zflip6, 34 api
Screenshots (for UI changes only)

Need help? See https://support.google.com/android/answer/9075928

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