GML: temptative fix for crash on certain xlink:href with GML_SKIP_RESOLVE_ELEMS=NONE (#5417)

git-svn-id: https://svn.osgeo.org/gdal/trunk@27035 f0d54148-0727-0410-94bb-9a71ac55c965
Merge branch 'trunk' into trunk_travis_macosx