Tie displayed incorrectly at start of system

As mentioned, there are cases where the same happens in 3.0.5, most of those were fixed as per #287022: Tie position incorect over line break without clef. However, a different fix of mine for an unrelated issue (#281024: Invisible staves inappropriately factored into note spacing) introduced a new case where this fails. That's because my original fix used prevEnabled() to find the segment to start drawing from, but now it really needs to use prevActive(). Otherwise, you get bad results if the key is C on all visible staves but you have invisible staves with a different key. On top of that, the width calculation might need a tuneup too.

Attached is a case that works in 3.0.5 but fails in 3.1. Load into 3.0.5 and you get this:

That's actually too much space, I think because we are paying attention to a key signature segment with nothing on it for the visible staves. But in 3.1, because we no longer even lay that segment out, you get this:

I should note you actually first get a kind of curious version where the tie is drawn over the clef, looks like maybe a cool optimization, but it redraws itself on the next layout to this.

https://github.com/musescore/MuseScore/pull/5062