JPEG: allow fallback to PAM to read GCPs; give priority to PAM GeoTransform if it exists and other source of geotransform (.wld, .tab) also exists (#5352)

git-svn-id: https://svn.osgeo.org/gdal/trunk/gdal@26840 f0d54148-0727-0410-94bb-9a71ac55c965