DistributionEditor: set lower bound for mean spinbox

This MR resolves #473 (closed)

The mean value of wavelength distributions cannot be set to less than the value double::min anymore in the DistributionEditor.

GUI/Model/Descriptor/DistributionItems.cpp

@@ -97,9 +97,9 @@ void DistributionItem::readFrom(QXmlStreamReader* r)
 // --------------------------------------------------------------------------------------------- //
 
 SymmetricResolutionItem::SymmetricResolutionItem(double mean, int decimals,
-                                                 const QString& meanLabel)
+                                                 const QString& meanLabel, const RealLimits limit)
 {
-    m_mean.init(meanLabel, "", mean, Unit::unitless, decimals, RealLimits::limitless(), "mean");
+    m_mean.init(meanLabel, "", mean, Unit::unitless, decimals, limit, "mean");
 }
 
 void SymmetricResolutionItem::setUnit(const variant<QString, Unit>& unit)
@@ -150,6 +150,11 @@ void SymmetricResolutionItem::readFrom(QXmlStreamReader* r)
     }
 }
 
+void SymmetricResolutionItem::setMeanLowerLimit(double lowerLimit)
+{
+    m_mean.setLimits(RealLimits::lowerLimited(lowerLimit));
+}
+
 // --------------------------------------------------------------------------------------------- //
 
 DistributionNoneItem::DistributionNoneItem()