Fix custom video not opening in full-screen mode

[ashiagr]

Fixes #64

Description

This PR opens the full-screen player when a custom file (or a UserEpisode) of video type is played. Previously, the player retained the mini mode.

It does that by finding the Playable instance (which looks for a UserEpisode when a normal Episode is not found) before checking if it is a video file.

To Test

1. Launch the app and go to Profile -> Files.
2. Add a custom MP4 video file.
3. Play the custom MP4 file.
4. ✅ Notice that the player comes in full-mode.

device-2022-09-12-131745.mp4

Checklist

• Should this change be included in the release notes? If yes, please add a line in CHANGELOG.md
• Have you tested in landscape?
• Have you tested accessibility with TalkBack? N/A
• Have you tested in different themes? N/A
• Does the change work with a large display font? N/A
• Are all the strings localized? N/A
• Could you have written any new tests? N/A
• Did you include Compose previews with any components? N/A

[mchowning]

Nice fix @ashiagr !