allow DoubleDescriptor in const calls

GUI/Model/Types/DoubleDescriptor.cpp

@@ -70,11 +70,11 @@ DoubleDescriptor::DoubleDescriptor(const QString& label, const QString& tooltip,
 {
 }
 
-DoubleDescriptor::DoubleDescriptor(const QString& label, double* var,
+DoubleDescriptor::DoubleDescriptor(const QString& label, const double* var,
                                    const variant<QString, Unit>& unit)
     : DoubleDescriptor(
-        label, "", 3, RealLimits::nonnegative(), [=](double v) { *var = v; }, [=] { return *var; },
-        unit)
+        label, "", 3, RealLimits::nonnegative(), [=](double v) { *const_cast<double*>(var) = v; },
+        [=] { return *var; }, unit)
 {
 }
 

GUI/Model/Types/DoubleDescriptor.h

@@ -51,7 +51,7 @@ public:
     //! Only for easier migration. Should be removed after SessionItem refactoring.
     DoubleDescriptor(const QString& label, SessionItem* item, const variant<QString, Unit>& unit);
 
-    DoubleDescriptor(const QString& label, double* var, const variant<QString, Unit>& unit);
+    DoubleDescriptor(const QString& label, const double* var, const variant<QString, Unit>& unit);
 
     //! Operates on any kind of storage (e.g. session items), by using setter/getter methods
     DoubleDescriptor(QString label, QString tooltip, int decimals, const RealLimits& limits,