Fix QgsCurvePolygon sip bindings

Author: manisandro

python/core/geometry/qgscurvepolygonv2.sip

@@ -80,7 +80,7 @@ class QgsCurvePolygonV2: public QgsSurfaceV2
     virtual int vertexCount( int /*part*/ = 0, int ring = 0 ) const;
     virtual int ringCount( int /*part*/ = 0 ) const;
     virtual int partCount() const;
-    virtual QgsPointV2 vertexAt( QgsVertexId id ) const;
+    virtual QgsPointV2 vertexAt( const QgsVertexId& id ) const;
 
     virtual bool addZValue( double zValue = 0 );
     virtual bool addMValue( double mValue = 0 );