Cannot send video - Sandbox deny file-issue-extension

It seems like Riot will fail sending a video if the video file name extension ends in `.medium.mp4` which is the extension when the file is stored in iCloud and isn't downloaded locally on device. Possible iOS bug?

```
error 20:31:35.336198 -0500 kernel Sandbox: Riot(8688) deny(1) file-issue-extension target:/private/var/mobile/Media/PhotoData/Metadata/DCIM/106APPLE/IMG_6845.medium.MP4 class:com.apple.mediaserverd.read
default 20:31:35.347438 -0500 Riot 🎥 AVPlayerCurrentItemDidChangeNotification
default 20:31:35.347487 -0500 Riot ⎣ ReasonRemoveFromPlayqueue
default 20:31:35.347881 -0500 Riot [MXTools] convertVideoToMP4: Video export failed. exportSession.status: 4
```

As a workaround you can force iOS to download the file and then it will send properly. Easiest way to do this is to use the Riot share sheet extension rather than uploading it inside of the app.