fix #296995: use a more reliable way to prevent layout from altering CmdState

Author: dmitrio95

libmscore/cmd.cpp

@@ -277,11 +277,9 @@ void Score::update(bool resetCmdState)
             CmdState& cs = ms->cmdState();
             ms->deletePostponed();
             if (cs.layoutRange()) {
-                  cs.lock();
                   for (Score* s : ms->scoreList())
                         s->doLayoutRange(cs.startTick(), cs.endTick());
                   updateAll = true;
-                  cs.unlock();
                   }
             }
 

libmscore/layout.cpp

@@ -4334,12 +4334,25 @@ void Score::doLayout()
       doLayoutRange(Fraction(0,1), Fraction(-1,1));
       }
 
+//---------------------------------------------------------
+//   CmdStateLocker
+//---------------------------------------------------------
+
+class CmdStateLocker {
+      Score* score;
+   public:
+      CmdStateLocker(Score* s) : score(s) { score->cmdState().lock(); }
+      ~CmdStateLocker() { score->cmdState().unlock(); }
+      };
+
 //---------------------------------------------------------
 //   doLayoutRange
 //---------------------------------------------------------
 
 void Score::doLayoutRange(const Fraction& st, const Fraction& et)
       {
+      CmdStateLocker cmdStateLocker(this);
+
       Fraction stick(st);
       Fraction etick(et);
       Q_ASSERT(!(stick == Fraction(-1,1) && etick == Fraction(-1,1)));