Describe the bug
GIMP plugin fails to load truncated progressive files that djxl can understand

To Reproduce
Steps to reproduce the behavior:
Encode an image progressively.
Truncate it.
Try to load it in GIMP.

Expected behavior
The image to load in GIMP.

Environment

• OS: GNU/Linux
• Compiler version: gcc (Ubuntu 11.2.0-19ubuntu1) 11.2.0
• CPU type: x86_64
• cjxl/djxl version string: v0.8.0 99b0721 [AVX3,AVX2,SSE4,SSSE3,Unknown]
  Copyright (c) the JPEG XL Project