[GeoCad] Undef Handle only if we do not need it:

Otherwise we get compilation errors:
In file included from /usr/include/oce/Handle_Interface_TypedValue.hxx:11:0,
                 from /usr/include/oce/Handle_Interface_Static.hxx:11,
                 from /usr/include/oce/Interface_Static.hxx:11,
                 from /mnt/build/jenkins/wsincr/LABEL/ROOT-centos7/SPEC/default/root/geom/geocad/src/TOCCToStep.cxx:38:
/usr/include/oce/Handle_MoniTool_TypedValue.hxx:14:27: error: aggregate ‘Handle Standard_Type’ has incomplete type and cannot be defined
 class Handle(Standard_Type);
                           ^