KRearrangeColumnsProxyModel: fix crash when there's no source model

autotests/krearrangecolumnsproxymodeltest.cpp

@@ -65,6 +65,16 @@ private Q_SLOTS:
         // showModel(&mod);
     }
 
+    void shouldShowNothingIfNoSourceModel()
+    {
+        // Given a rearrange-columns proxy with no source model
+        KRearrangeColumnsProxyModel pm;
+
+        // Then the proxy should show nothing (no columns selected)
+        QCOMPARE(pm.rowCount(), 0);
+        QCOMPARE(pm.columnCount(), 0);
+    }
+
     void shouldShowNothingIfNoColumnSelection()
     {
         // Given a rearrange-columns proxy

src/krearrangecolumnsproxymodel.cpp

@@ -44,12 +44,18 @@ void KRearrangeColumnsProxyModel::setSourceColumns(const QVector<int> &columns)
 int KRearrangeColumnsProxyModel::columnCount(const QModelIndex &parent) const
 {
     Q_UNUSED(parent);
+    if (!sourceModel()) {
+        return 0;
+    }
     return d_ptr->m_sourceColumns.count();
 }
 
 int KRearrangeColumnsProxyModel::rowCount(const QModelIndex &parent) const
 {
     Q_ASSERT(parent.isValid() ? parent.model() == this : true);
+    if (!sourceModel()) {
+        return 0;
+    }
     // The parent in the source model is on column 0, whatever swapping we are doing
     const QModelIndex sourceParent = mapToSource(parent).sibling(parent.row(), 0);
     return sourceModel()->rowCount(sourceParent);