Fix some bugs on FLUTTER video download app

My flutter app is in development. It's a video download app – gets videos from a popular video app. It retrieves videos in packs of 30 or all remaining videos. Once videos are retrieved, user selects desired videos for download. However, there are several bugs getting videos (not downloading). It may be the case that they can be traced to a common cause. For the most part it gets the videos.

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FIXED BUDGET, NON-NEGOTIABLE