KRearrangeColumnsProxyModel: reimplement sibling() so it works as expected

autotests/krearrangecolumnsproxymodeltest.cpp

@@ -121,6 +121,9 @@ private Q_SLOTS:
         QCOMPARE(pm.mapToSource(pm.index(0, 0)).column(), 2); // column 0 points to C
         QCOMPARE(pm.mapToSource(pm.index(0, 1)).column(), 3); // column 1 points to D
 
+        QCOMPARE(pm.sibling(0, 1, pm.index(0, 0)).column(), 1);
+        QCOMPARE(pm.sibling(0, 0, pm.index(0, 1)).column(), 0);
+
         QCOMPARE(extractRowTexts(&pm, 0), QStringLiteral("CDBA"));
         QCOMPARE(extractRowTexts(&pm, 0, pm.index(0, 0)), QStringLiteral("opnm"));
         QCOMPARE(extractRowTexts(&pm, 1, pm.index(0, 0)), QStringLiteral("strq"));

src/krearrangecolumnsproxymodel.cpp

@@ -97,6 +97,13 @@ QVariant KRearrangeColumnsProxyModel::headerData(int section, Qt::Orientation or
     }
 }
 
+QModelIndex KRearrangeColumnsProxyModel::sibling(int row, int column, const QModelIndex &idx) const
+{
+    if (column >= d_ptr->m_sourceColumns.count())
+        return QModelIndex();
+    return index(row, column, idx.parent());
+}
+
 QModelIndex KRearrangeColumnsProxyModel::mapFromSource(const QModelIndex &sourceIndex) const
 {
     if (!sourceIndex.isValid()) {

src/krearrangecolumnsproxymodel.h

@@ -87,6 +87,9 @@ public:
     /// @reimp
     QVariant headerData(int section, Qt::Orientation orientation, int role = Qt::DisplayRole) const Q_DECL_OVERRIDE;
 
+    /// @reimp
+    QModelIndex sibling(int row, int column, const QModelIndex &idx) const Q_DECL_OVERRIDE;
+
 private:
     int proxyColumnForSourceColumn(int sourceColumn) const;
     int sourceColumnForProxyColumn(int proxyColumn) const;