OpenFileGDB: fix and test a few interactions of GetFeature(), SetNextByIndex() and SetAttributeFilter() with in-memory spatial index building

git-svn-id: https://svn.osgeo.org/gdal/trunk@26844 f0d54148-0727-0410-94bb-9a71ac55c965
Merge branch 'trunk' into trunk_travis_macosx