don't crash on export of ooo52825-1.doc to .docx

Change-Id: I944f65c9bf1cf7cc39e674bab602dbf2d499317c

oox/source/export/vmlexport.cxx

@@ -523,7 +523,7 @@ void VMLExport::Commit( EscherPropertyContainer& rProps, const Rectangle& rRect
                                     // See EscherPropertyContainer::CreateCustomShapeProperties, by default nSeg is simply the number of points.
                                     // FIXME: we miss out a significant amount of complexity from
                                     // the above method here, and do some rather odd things to match.
-                                    int nElems = aVertices.nPropSize / ( nPointSize * 2);
+                                    int nElems = !nPointSize ? 0 : aVertices.nPropSize / (nPointSize * 2);
                                     if (nSeg > nElems)
                                     {
                                         SAL_WARN("oox", "Busted escher export " << nSeg << "vs . " << nElems << " truncating point stream");