S57: some more robustness fixes

git-svn-id: https://svn.osgeo.org/gdal/trunk/gdal@25834 f0d54148-0727-0410-94bb-9a71ac55c965
S57: some more robustness fixes

git-svn-id: https://svn.osgeo.org/gdal/trunk/gdal@25835 f0d54148-0727-0410-94bb-9a71ac55c965