Regroup Rhythms doesn't work when measure starts with tuplet segment

Reproducing the issue:
1. Attach a simple score starting with a tuplet of rests.

2. Regroup the score.
3. The score remains unaffected.

However, in the example it should regroup the tuplet with the second quarter count rest, to form half a count rest.

The root cause is Score::regroupNotesAndRests() doesn't take tuplets into account when it is the starting segment. When simple changing the if (curr->isRest() && !(curr -> tuplet()) && !(toRest(curr) -> isGap())) case by removing the !(curr->tuplet()) condition, it will no longer work for tuplets containing a note or a nested tuplet, because the loop will then also consider the second segment in the tuplet and recursively handle this.