fix: ignore empty accept entries

[feritcemkahraman]

A trailing comma or blank array entry can accept an unrelated file whose MIME type is unknown. For example, accept({ name: "document.pdf", type: "" }, ".png,") currently returns true because the empty entry matches the empty MIME type.

Ignore blank entries before matching. If no entries remain, treat the list like the already-supported empty string/empty array and accept any file. Valid extension and MIME matching stays the same.

Validation:

• Seven new regressions fail before the source fix, covering leading/trailing commas, blank array entries and entirely empty lists.
• All 17 Vitest tests pass with 100% statement, branch, function and line coverage.
• Type check, oxlint, type-aware oxlint and repository format check pass.
• tsdown builds ESM/CJS and declarations; size-limit passes (558 B ESM, 560 B CJS brotlied; 2 kB budget).
• git diff --check passes.

On Windows, the npm prebuild cleanup (rm -rf) is unavailable, so the same build and size tools were run with npm exec -- tsdown and npm exec -- size-limit. No package scripts or dependencies were changed.

[github-actions]

🎉 This PR is included in version 4.0.1 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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