Initialize bIgnore flag in OGRFieldDefn( const char * pszNameIn, OGRFieldType eTypeIn ) constructor (#5164)

git-svn-id: https://svn.osgeo.org/gdal/trunk@26201 f0d54148-0727-0410-94bb-9a71ac55c965
Merge branch 'trunk' of github.com:rouault/gdal into trunk_with_coverage