Use panSrcBands when accessing the source data

[tomhughes]

Commit 65fd09c introduced an optimisation when there is only a single band being read, but when reading from the source it is using panDstBands to find the number of that band which will be wrong if the band number is different in the source and destination file.

This is a simple test case, extracted from one of the node-gdal tests, which demonstrates the problem:

#include <stdlib.h>

#include <gdal_priv.h>
#include <gdalwarper.h>
#include <ogrsf_frmts.h>

int main(int argc, char **argv)
{
  GDALAllRegister();

  GDALDriver *mem = GetGDALDriverManager()->GetDriverByName("MEM");
  GDALDataset *src = (GDALDataset *)GDALOpenEx("./rpm/BUILD/node-gdal-0.9.6-fedora/test/data/sample.tif", GDAL_OF_READONLY, NULL, NULL, NULL);
  GDALDataset *dst = mem->Create("temp", 208, 127, 2, GDT_Int16, nullptr);
  GDALWarpOptions *options = GDALCreateWarpOptions();
  int srcBands[1] = { 1 };
  int dstBands[1] = { 2 };
  double transform[6] = { -110.3765574645805, 0.0005, 0, 44.59676651822825, 0, -0.0005 };

  options->hSrcDS = src;
  options->hDstDS = dst;
  options->nDstAlphaBand = 1;
  options->nBandCount = 1;
  options->panSrcBands = srcBands;
  options->panDstBands = dstBands;

  const char *s_srs_wkt = src->GetProjectionRef();
  char *t_srs_wkt;

  OGRSpatialReference::GetWGS84SRS()->exportToWkt(&t_srs_wkt);

  dst->SetProjection(t_srs_wkt);
  dst->SetGeoTransform(transform);

  GDALReprojectImage(options->hSrcDS, s_srs_wkt,
                     options->hDstDS, t_srs_wkt,
                     options->eResampleAlg, 0.0, 0,
                     nullptr, nullptr, options);

  exit(0);
}

without this change that will error as it tries to read band 2 from a source that only has one band:

ERROR 5: ./rpm/BUILD/node-gdal-0.9.6-fedora/test/data/sample.tif: GDALDataset::GetRasterBand(2) - Illegal band #

[rouault]

Committed in trunk r41327 and branches/2.2 r41328. Thanks !