MITAB: fix opening in update mode of non-spatial layers (i.e. without .map) (#5718): note update operations on such layers untested and likely need fixes

git-svn-id: https://svn.osgeo.org/gdal/trunk@27912 f0d54148-0727-0410-94bb-9a71ac55c965
Merge branch 'trunk' into trunk_vc12