programs: fix zstd -l infinite loop on a large skippable frame

[ilyas-mallah]

What and why

zstd -l never returns on a file with a skippable frame whose Frame_Size is 0xFFFFFFF8. In FIO_analyzeFrames(), 8 + frameSize is 32-bit unsigned and wraps to 0, so the seek goes backwards and the loop rereads the same header forever.

Where long is 32 bits, the cast also breaks valid files with a skippable frame of 2 GB or more. A 32-bit Linux build fails on a file with a 3 GiB skippable frame with Error: could not find end of skippable frame. 64-bit Windows has the same 32-bit long.

With the offset computed in 64 bits, the crafted file is reported as truncated, and the 3 GiB file lists as 2 frames with 1 skip in the 32-bit build. To reproduce:

printf '\x50\x2A\x4D\x18\xF8\xFF\xFF\xFFpayload' > skip.zst
zstd -l skip.zst

The new playTests.sh case uses that file, and make -C tests test-zstd and the cli-tests pass.

Checklist

• I searched open pull requests and issues: this problem is not already being addressed.
• Bug fix: it comes with a reproducer or a test that fails without the fix.
• Performance change: numbers from repeated runs are included, with CPU, compiler, flags and data.
• I stated below whether AI or other automated tools were used.

Tools used

AI usage: Claude Code helped with the test runs and the 32-bit build. I found the loop, made the fix, and validated every change.

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