Timeline is broken when not initialized with a screenplay

[jbilcke-hf]

Context

When we start with an empty timeline, some operations such as loading a mp3 or generating a story with the assistant appear to "break", or maybe "not initialize" the timeline (we won't be able to click in the top tipeline to position the cursor for instance)

Solution

I don't know what the cause of issue is exactly 😅
need to investigate