#5357: Add OGR_G_SetPointCount and OGR_G_SetPoints functions to API C

From: Alvaro Huarte <ahuarte47@yahoo.es>

git-svn-id: https://svn.osgeo.org/gdal/trunk@26858 f0d54148-0727-0410-94bb-9a71ac55c965
#5357: fix VALIDATE_POINTER0 macro

From: Alvaro Huarte <ahuarte47@yahoo.es>

git-svn-id: https://svn.osgeo.org/gdal/trunk@26859 f0d54148-0727-0410-94bb-9a71ac55c965