JPEGXL images not cropping/bucketing correctly

All JPEGXL images gets placed into the same bucket regardless of image size or bucket settings with a mean of 0.0.

Without --bucket_no_upscale the bucket has my selected resolution of 768,768.

With --bucket_no_upscale the bucket has the resolution of the negative size of the bucket_reso_steps, -128,-128.

After running some testing and training, images are not cropped but are stretched to fit.

No source file or test is identified; start by reproducing JPEGXL training with the reported bucket settings, including --bucket_no_upscale, bucket_reso_steps, and 768,768 resolution. Trace the image bucketing and cropping path, then verify that JPEGXL images receive size-appropriate buckets, report a nonzero mean where expected, and are cropped rather than stretched.

Written by the indexing model from the issue text.