Video files not loading.

I'm not able to use an `mp4` video file in ZeroNet for some reason. **I was able to sign and update the site in another node** but I'm not able to play the video.

@imachug can you look into this?

Start by reproducing the reported inability to load or play an mp4 video in ZeroNet, comparing it with the node where the site was signed and updated successfully. Trace the relevant video-loading path; done means the same video can be played reliably in ZeroNet.

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