VRT: GDALDatasetRasterIO (Read) problem with buffer initialization

[dengo]

I recently noticed that, when reading a part of a VRT (GDALDatasetRasterIO) that is not covered by any input raster and the NODATA Value is not defined in the VRT, the pixels in the buffer are not set at all. Because I reuse the buffer and don't initialize it myself I get 'random' results.

As I said above, this problem does not happen when the NODATA Value is defined, but still this is probably not the desired behavior.

I started noticing this problem with GDAL 2.2. Perhaps it has something to do with the changelog entry for the VRT driver "avoid buffer initialization in RasterIO() when possible (replace ancient and likely broken concept of bEqualAreas)"

Also this problem does not seem to occur when using GDALRasterIO instead.

[Even Rouault]

In 39580:

VRT: fix uninitialized buffer in areas without sources when using non pixel packed spacing (fixes #6965)

[Even Rouault]

In 39581:

VRT: fix uninitialized buffer in areas without sources when using non pixel packed spacing (fixes #6965)

[dengo]

Thanks for the quick fix.