fix #298061: fix a crash on "set as style" if score ends with a frame

 - Don't pass staff number to adjustCanvasPosition if trying to
   adjust viewport to a frame. This avoids a crash itself.
 - Implement a more robust approach to determine a measure relevant
   to the current edit operation in CmdState. This avoids trying to
   unnecessarily jump to the frame at the end of a score.

libmscore/cmd.cpp

@@ -92,7 +92,8 @@ void CmdState::reset()
       _endStaff = -1;
       _el = nullptr;
       _oneElement = true;
-      _elIsMeasureBase = false;
+      _mb = nullptr;
+      _oneMeasureBase = true;
       _locked = false;
       }
 
@@ -128,6 +129,19 @@ void CmdState::setStaff(int st)
             _endStaff = st;
       }
 
+//---------------------------------------------------------
+//   setMeasureBase
+//---------------------------------------------------------
+
+void CmdState::setMeasureBase(const MeasureBase* mb)
+      {
+      if (!mb || _mb == mb || _locked)
+            return;
+
+      _oneMeasureBase = !_mb;
+      _mb = mb;
+      }
+
 //---------------------------------------------------------
 //   setElement
 //---------------------------------------------------------
@@ -137,20 +151,11 @@ void CmdState::setElement(const Element* e)
       if (!e || _el == e || _locked)
             return;
 
-      // prefer measures and frames as edit targets
-      const bool oldIsMeasureBase = _elIsMeasureBase;
-      const bool newIsMeasureBase = e->isMeasureBase();
-      if (newIsMeasureBase && !oldIsMeasureBase) {
-            _oneElement = true;
-            return;
-            }
-      else if (oldIsMeasureBase && !newIsMeasureBase)
-            return; // don't remember the new element
-      else
-            _oneElement = !_el;
-
+      _oneElement = !_el;
       _el = e;
-      _elIsMeasureBase = newIsMeasureBase;
+
+      if (_oneMeasureBase)
+            setMeasureBase(e->findMeasureBase());
       }
 
 //---------------------------------------------------------
@@ -161,6 +166,21 @@ void CmdState::unsetElement(const Element* e)
       {
       if (_el == e)
             _el = nullptr;
+      if (_mb == e)
+            _mb = nullptr;
+      }
+
+//---------------------------------------------------------
+//   element
+//---------------------------------------------------------
+
+const Element* CmdState::element() const
+      {
+      if (_oneElement)
+            return _el;
+      if (_oneMeasureBase)
+            return _mb;
+      return nullptr;
       }
 
 //---------------------------------------------------------

libmscore/score.h

@@ -260,11 +260,14 @@ class CmdState {
       int _startStaff = -1;
       int _endStaff = -1;
       const Element* _el = nullptr;
+      const MeasureBase* _mb = nullptr;
       bool _oneElement = true;
-      bool _elIsMeasureBase = false;
+      bool _oneMeasureBase = true;
 
       bool _locked = false;
 
+      void setMeasureBase(const MeasureBase* mb);
+
    public:
       LayoutFlags layoutFlags;
 
@@ -286,7 +289,7 @@ class CmdState {
       Fraction endTick() const   { return _endTick; }
       int startStaff() const { return _startStaff; }
       int endStaff() const { return _endStaff; }
-      const Element* element() const { return _oneElement ? _el : nullptr; }
+      const Element* element() const;
 
       void lock() { _locked = true; }
       void unlock() { _locked = false; }

mscore/scoreview.cpp

@@ -4926,7 +4926,7 @@ void ScoreView::moveViewportToLastEdit()
 
       const Element* viewportElement = (editElement && editElement->bbox().isValid() && !mb->isMeasure()) ? editElement : mb;
 
-      const int staff = sc->isMaster() ? st.startStaff() : -1; // TODO: choose the closest staff to the current viewport?
+      const int staff = sc->isMaster() && mb->isMeasure() ? st.startStaff() : -1; // TODO: choose the closest staff to the current viewport?
       adjustCanvasPosition(viewportElement, /* playback */ false, staff);
       }
 }