Fix for the cursor position

[C0D3D3V]

A bug to solve for the future maintainer :)

The position of the cursor is kind of wrong calculated. https://github.com/tilmanmoser/bbb-video-download/blob/93b894c60d8f34c4e5087e5f09be88e5fe3a9827/src/modules/slides.js#L229-L232

It should be more like this:

https://github.com/bigbluebutton/bbb-playback/blob/ba7e67d8c352d6a5383cc42442178a880db10da7/src/components/presentation/cursor.js#L18-L19

pos_X = current_view_box.x + (action.x * current_view_box.width),
pos_Y = current_view_box.y + (action.y * current_view_box.height),

At least bbb and my bbb-dl uses this calculation, and they look correct.

I also want to point out, that bbb finally published there own script to render the presentation video (without deskshare/webcams) https://github.com/bigbluebutton/bbb-presentation-video. Maybe this can be useful for the future maintainer :D