GPKG: fix crash, memory error and memory leaks (#5335)

git-svn-id: https://svn.osgeo.org/gdal/trunk@26866 f0d54148-0727-0410-94bb-9a71ac55c965
GPKG: initialize variable

git-svn-id: https://svn.osgeo.org/gdal/trunk@26867 f0d54148-0727-0410-94bb-9a71ac55c965
ogr_formats.html: move GeoPackage line

git-svn-id: https://svn.osgeo.org/gdal/trunk@26868 f0d54148-0727-0410-94bb-9a71ac55c965