Merge pull request #9033 from mhugo/fix_20831

Fix "Allow null" in range widget (fixes #20831)

Author: Hugo Mercier

src/gui/editorwidgets/qgsrangewidgetwrapper.cpp

@@ -146,7 +146,12 @@ void QgsRangeWidgetWrapper::initWidget( QWidget *editor )
     if ( allowNull )
     {
       int stepval = step.isValid() ? step.toInt() : 1;
-      minval -= stepval;
+      int newMinval = minval - stepval;
+      // make sure there is room for a new value (i.e. signed integer does not overflow)
+      if ( newMinval < minval )
+      {
+        minval = newMinval;
+      }
       mIntSpinBox->setValue( minval );
       QgsSpinBox *intSpinBox( qobject_cast<QgsSpinBox *>( mIntSpinBox ) );
       if ( intSpinBox )