common : fix split model migration (#21019)

common : fix split model migration (#21019)

Sadly the manifest does not list all required files, i honestly thought
it was the case

Without the files listed we don't have the sha256, so if the first file
is valid, and all others have the correct size, then we can assume we
are good and do the migration...

Here my test:

    $ find /home/angt/.cache/llama.cpp
    /home/angt/.cache/llama.cpp
    /home/angt/.cache/llama.cpp/angt_test-split-model-stories260K_stories260K-f32-00002-of-00002.gguf
    /home/angt/.cache/llama.cpp/angt_test-split-model-stories260K_stories260K-f32-00001-of-00002.gguf
    /home/angt/.cache/llama.cpp/angt_test-split-model-stories260K_stories260K-f32-00001-of-00002.gguf.etag
    /home/angt/.cache/llama.cpp/angt_test-split-model-stories260K_stories260K-f32-00002-of-00002.gguf.etag
    /home/angt/.cache/llama.cpp/manifest=angt=test-split-model-stories260K=latest.json

    $ build/bin/llama-server
    ================================================================================
    WARNING: Migrating cache to HuggingFace cache directory
      Old cache: /home/angt/.cache/llama.cpp/
      New cache: /home/angt/.cache/huggingface/hub
    This one-time migration moves models previously downloaded with -hf
    from the legacy llama.cpp cache to the standard HuggingFace cache.
    Models downloaded with --model-url are not affected.
    ================================================================================
    migrate_file: migrated angt_test-split-model-stories260K_stories260K-f32-00001-of-00002.gguf -> /home/angt/.cache/huggingface/hub/models--angt--test-split-model-stories260K/snapshots/68c3ea2061e8c7688455fab07597dde0f4d7f0db/stories260K-f32-00001-of-00002.gguf
    migrate_file: migrated angt_test-split-model-stories260K_stories260K-f32-00002-of-00002.gguf -> /home/angt/.cache/huggingface/hub/models--angt--test-split-model-stories260K/snapshots/68c3ea2061e8c7688455fab07597dde0f4d7f0db/stories260K-f32-00002-of-00002.gguf
    migrate_old_cache_to_hf_cache: migration complete, deleting manifest: /home/angt/.cache/llama.cpp/manifest=angt=test-split-model-stories260K=latest.json

    $ find /home/angt/.cache/llama.cpp /home/angt/.cache/huggingface
    /home/angt/.cache/llama.cpp
    /home/angt/.cache/huggingface
    /home/angt/.cache/huggingface/hub
    /home/angt/.cache/huggingface/hub/models--angt--test-split-model-stories260K
    /home/angt/.cache/huggingface/hub/models--angt--test-split-model-stories260K/blobs
    /home/angt/.cache/huggingface/hub/models--angt--test-split-model-stories260K/blobs/50d019817c2626eb9e8a41f361ff5bfa538757e6f708a3076cd3356354a75694
    /home/angt/.cache/huggingface/hub/models--angt--test-split-model-stories260K/blobs/7b273e1dbfab11dc67dce479deb5923fef27c39cbf56a20b3a928a47b77dab3c
    /home/angt/.cache/huggingface/hub/models--angt--test-split-model-stories260K/refs
    /home/angt/.cache/huggingface/hub/models--angt--test-split-model-stories260K/refs/main
    /home/angt/.cache/huggingface/hub/models--angt--test-split-model-stories260K/snapshots
    /home/angt/.cache/huggingface/hub/models--angt--test-split-model-stories260K/snapshots/68c3ea2061e8c7688455fab07597dde0f4d7f0db
    /home/angt/.cache/huggingface/hub/models--angt--test-split-model-stories260K/snapshots/68c3ea2061e8c7688455fab07597dde0f4d7f0db/stories260K-f32-00002-of-00002.gguf
    /home/angt/.cache/huggingface/hub/models--angt--test-split-model-stories260K/snapshots/68c3ea2061e8c7688455fab07597dde0f4d7f0db/stories260K-f32-00001-of-00002.gguf

Signed-off-by: Adrien Gallouët <redacted>