Describe the bug
See, #1863 (comment)
In the Wikipedia.jxl when reading the image with coalescing turned off, we see images that appear are of duration 0 and appear to be empty.

To Reproduce
Compile gimp plugin at ddda9b2 and load Wikipedia.jxl with that. (Or modify libjxl-info to also get those frames by setting coalescing to false there as well.)

Expected behavior
Frames with no information (like of duration 0, with no content) shouldn't appear, even with coalescing set to false.

Additional context
Might not really be a bug, but simply something we are not seeing in those frames that appear to be empty.