[GStreamer] Seek on loadedmetadata is ignored

[Alicia Boya García]

I was writing a test for an unrelated bug when I found this.

        const eventWatcher = new EventWatcher(test, video, ["loadedmetadata", "seeked", "ended"]);
        await eventWatcher.wait_for("loadedmetadata");
        assert_equals(video.videoWidth, 320, "width when the video is loaded");
        assert_equals(video.videoHeight, 240, "height when the video is loaded");
        video.currentTime = 5;
        video.play();
        await eventWatcher.wait_for(["seeked", "ended"]);

You would expect the video to start playing on t=5, but it starts on t=0 instead. That's a bug.

[Alicia Boya García]

This is in regular playback from an HTTP resource (not MSE).

[Fernando Jiménez Moreno]

I am not sure if this is exactly what you meant, but a test like this works for me:

```
        const video = document.querySelector('video');
        video.addEventListener('loadedmetadata', event => {
            console.log('onloadedmetadata received');
            console.log('Seeking to t=15');
            video.currentTime = 15;
            video.play();
        });
        video.addEventListener('seeked', event => {
            console.log('Seek received');
        });
```

The logs are properly shown and video starts at t=15 (if autoplay is allowed)