Merge pull request #27458 from xaos-cz:4.x

imread: GDAL multi-channel support #27458 

- tested on 30-channel FITS and 186-channel ENVI files

### 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
      Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake

modules/imgcodecs/src/grfmt_gdal.cpp

@@ -408,6 +408,9 @@ bool GdalDecoder::readData( Mat& img ){
         case GCI_AlphaBand:
             color = 3;
             break;
+        case GCI_Undefined:
+            color = c;
+            break;
         default:
             CV_Error(cv::Error::StsError, "Invalid/unsupported mode");
         }