Handle M/Z typed CurvePolygons in qgsgeometry_cast

Author: m-kuhn

src/core/geometry/qgscurvepolygon.h

@@ -154,7 +154,7 @@ class CORE_EXPORT QgsCurvePolygon: public QgsSurface
       if ( !geom )
         return nullptr;
 
-      QgsWkbTypes::Type flatType = geom->wkbType();
+      QgsWkbTypes::Type flatType = QgsWkbTypes::flatType( geom->wkbType() );
       if ( flatType == QgsWkbTypes::CurvePolygon
            || flatType == QgsWkbTypes::Polygon
            || flatType == QgsWkbTypes::Triangle )