fix #41371: preserve score position when switching page/continuous view

mscore/musescore.cpp

@@ -4344,13 +4344,25 @@ void MuseScore::switchLayoutMode(int val)
       if (cs) {
             cs->startCmd();
             LayoutMode mode;
+            // find a measure to use as reference, if possible
+            QRectF view = cv->toLogical(QRect(0.0, 0.0, width(), height()));
+            MeasureBase* m = cs->measures()->first();
+            while (m && !view.intersects(m->canvasBoundingRect()))
+                  m = m->nextMM();
             if (val == 0)
                   mode = LayoutMode::PAGE;
             else
                   mode = LayoutMode::LINE;
             cs->undo(new ChangeLayoutMode(cs, mode));
             cv->loopUpdate(getAction("loop")->isChecked());
             cs->endCmd();
+            // adjustCanvasPosition often tries to preserve Y position
+            // but this doesn't make sense when switching modes
+            // also, better positioning is usually achieved if you start from the top
+            // and there is really no better place to position canvas if we were all the way off page previously
+            cv->pageTop();
+            if (m)
+                  cv->adjustCanvasPosition(m, false);
             endCmd();
             }
       }

mscore/scoreview.cpp

@@ -3648,7 +3648,7 @@ void ScoreView::pagePrev()
 void ScoreView::pageTop()
       {
       if (score()->layoutMode() == LayoutMode::LINE)
-            setOffset(0.0, yoffset());
+            setOffset(0.0, 0.0);
       else
             setOffset(10.0, 10.0);
       update();
@@ -3686,6 +3686,7 @@ void ScoreView::adjustCanvasPosition(const Element* el, bool playBack)
             return;
 
       if (score()->layoutMode() == LayoutMode::LINE) {
+
             if (!el)
                   return;