Fix #291688, Fix: #285855

[njvdberg]

Resolves: https://musescore.org/en/node/291688
Resolves: https://musescore.org/en/node/285855

In Excerpt::cloneStaves() clones TimeSig's and KeySig's if source staff 1 is not mapped to a track. To prevent copying of precaution segments only TimeSig's and KeySig's at the beginning of the measure are copied. This is done by getting the tick and clone the element when it is at the start of the measure only.
However, the test was using element->tick() instead of segment->rtick().

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[MarcSabatella]

This is crazy - seriously, all this time it was a one-line fix? I figured it would be relatively simple, but... wow.

I take it that https://musescore.org/en/node/283964 is not fixed by this, that seems the other critical issue with this feature. Having this working for 3.5 would be very good...

[njvdberg]

Easy indeed :-). At this very moment I'm looking into #281666 - Parts Dialog Problem with Voices, this look pretty straight forward too.
Then I'll have a look at #283964 - Linked parts for single voices don't work. I don't it is already solved but will find out soon.

[RobFog]

/OCD The commit message and PR title could be made more consistent by removing the colon after the second "fix". Probably also makes sense to lower-case the second "fix".