forcepoint #33 ensure payload is a EMFPPath

Change-Id: I0a9f332cc66e43caa4e1611006fa765cad063539
Reviewed-on: https://gerrit.libreoffice.org/51916Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
(cherry picked from commit 5795e68b)

cppcanvas/source/mtfrenderer/emfplus.cxx

@@ -1979,7 +1979,7 @@ namespace cppcanvas
 
                             SAL_INFO("cppcanvas.emf", "EMF+ FillPath slot: " << index);
 
-                            EMFPPath* path = static_cast<EMFPPath*>(aObjects[index]);
+                            EMFPPath* path = dynamic_cast<EMFPPath*>(aObjects[index]);
                             if (path)
                                 EMFPPlusFillPolygon(path->GetPolygon (*this), rFactoryParms, rState, rCanvas, flags & 0x8000, brushIndexOrColor);
                             else
@@ -2106,7 +2106,7 @@ namespace cppcanvas
                             SAL_INFO("cppcanvas.emf", "EMF+ DrawPath");
                             SAL_INFO("cppcanvas.emf", "EMF+\tpen: " << penIndex);
 
-                            EMFPPath* path = static_cast<EMFPPath*>( aObjects [flags & 0xff] );
+                            EMFPPath* path = dynamic_cast<EMFPPath*>( aObjects [flags & 0xff] );
                             if (path)
                                 EMFPPlusDrawPolygon(path->GetPolygon (*this), rFactoryParms, rState, rCanvas, penIndex);
                             else