Compile without warnings in ndef DEBUG mode (#5414)

git-svn-id: https://svn.osgeo.org/gdal/trunk@28165 f0d54148-0727-0410-94bb-9a71ac55c965
Initialize pointer to nullptr (#5414)

git-svn-id: https://svn.osgeo.org/gdal/trunk@28166 f0d54148-0727-0410-94bb-9a71ac55c965