--previous-build-manifest with different layer num causes panic

[antheas]

If the user provides a --previous-build-manifest to rpm-ostree compose container-encapsulate which has a different number of max-layers than what was requested, the following line panics:

ostree-rs-ext/lib/src/chunking.rs

Line 625 in 9a4743a

assert!(modified_build.len() <= bin_size.get() as usize);

Expected behavior would be to attempt to do the merge gracefully as far as this library is concerned. Failing that, rpm-ostree should emit a warning and ignore the previous manifest.

Context: I did a build that went from 100 layers to 50.