solidtest: Fix segfault in setExteriorShell test

For the pointer version, The `Polyhedralsurface` takes ownership of
the shell.

This fixes commit 481cce2.

test/unit/SFCGAL/SolidTest.cpp

@@ -21,6 +21,7 @@
 #include "SFCGAL/Kernel.h"
 
 #include "SFCGAL/Solid.h"
+#include "SFCGAL/PolyhedralSurface.h"
 #include "SFCGAL/TriangulatedSurface.h"
 #include "SFCGAL/io/wkt.h"
 #include "SFCGAL/algorithm/covers.h"
@@ -130,7 +131,7 @@ BOOST_AUTO_TEST_CASE(solidSetExteriorRingTest)
   BOOST_CHECK(!shell1->isEmpty());
   BOOST_CHECK(solid->isEmpty());
 
-  solid->setExteriorShell(shell1);
+  solid->setExteriorShell(shell1->as<PolyhedralSurface>());
   BOOST_CHECK_EQUAL(solid->numShells(), 1);
   BOOST_CHECK(!solid->isEmpty());
   BOOST_CHECK(algorithm::covers3D(solid->exteriorShell(), *shell1));