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gdal: skip raster band mapped to an out-of-range channel in readData - #29439 Repro: read a 3-band GDT_Byte raster (no palette) whose third band is tagged `GCI_AlphaBand`, via `imread(path, IMREAD_LOAD_GDAL)`. ASan reports a heap-buffer-overflow WRITE of size 1 at `grfmt_gdal.cpp:259`. Cause: an alpha band makes `readData` pass `color = 3`, but the `gdalChannels == 3 && image.channels() == 3` branch of `write_pixel` indexes `Vec3b[channel]` with no bound, so `channel == 3` stores one element past the 3-lane pixel. On the last pixel that lands past the Mat buffer. Fix (per review): `readData` checks the mapped color index against `img.channels()` in the band loop, before the pixel iteration. An out-of-range band is skipped as a whole with a `CV_LOG_WARNING` naming the band and range, instead of a silent per-pixel guard. Valid RGB rasters decode identically. ### Pull Request Readiness Checklist See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request - [x] I agree to contribute to the project under Apache 2 License. - [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV - [x] The PR is proposed to the proper branch - [ ] There is a reference to the original bug report and related work - [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable - [ ] The feature is well documented and sample code can be built with the project CMake