ECW ignores position (and other) data when it has an external file

[idos]

The GetGeoTransform method of ECWDataSet first checks if the data-set is using an external (via the GDALPamDataset class) coordinate system defintion (the code is a bit confusing, but that's what it does). But, in case there is only a coordinate definition and no geo-transform data in the PamDataset source, the method will fail, even if the geo-transform data is included in the ecw file's metadata. I think it should simply be changed so that in case GDALPanDataset returns an error, it will return its own GeoTransform matrix anyway (just like in the case there's no external coordinate system).

[Even Rouault]

r22589 /branches/1.8/gdal/frmts/ecw/ecwdataset.cpp: ECW: ensure we fallback to native geotransform if no pam override (#4131, backport of r22135)