code-Update wasi.ts

[romashka-btc]

Fix: Replaced logical OR (||) with nullish coalescing operator (??)

Changes

• Updated src/worker/wasi.ts:54 to use the nullish coalescing operator (??) for safer fallback handling.

  • Before:

    const contentType = response.headers.get("Content-Type") || "";

  • After:

    const contentType = response.headers.get("Content-Type") ?? "";

Purpose

• Ensured safer fallback behavior by using the nullish coalescing operator, which only falls back for null or undefined.