[bug] Custom protocol is not working in alpha.12+

[CrendKing]

Describe the bug

Thanks for fixing #7801. However, it seems the custom protocol, or at least the asset protocol, is also broken by the new alpha.12, which might be related to the previous issue.

In console's network tab, the request gets HTTP 400, with the error message "The filename, directory name, or volume label syntax is incorrect. (os error 123)".

Reverting to alpha.11 instantly fixes the issue.

Reproduction

1. pnpm create tauri-app --alpha.
2. Modify the main.ts to have a convertFileSrc. Modify tauri.conf.json as necessary.
3. Launch the app.

Expected behavior

The image from asset protocol should load.

Platform and versions

[✔] Environment
    - OS: Windows 10.0.22621 X64
    ✔ WebView2: 116.0.1938.76
    ✔ MSVC: Visual Studio Build Tools 2022
    ✔ rustc: 1.72.0 (5680fa18f 2023-08-23)
    ✔ Cargo: 1.72.0 (103a7ff2e 2023-08-15)
    ✔ rustup: 1.26.0 (5af9b9484 2023-04-05)
    ✔ Rust toolchain: stable-x86_64-pc-windows-msvc (environment override by RUSTUP_TOOLCHAIN)
    - node: 18.17.1
    - pnpm: 8.7.4
    - npm: 9.6.7

[-] Packages
    - tauri [RUST]: 2.0.0-alpha.14
    - tauri-build [RUST]: 2.0.0-alpha.8
    - wry [RUST]: 0.33.0
    - tao [RUST]: 0.22.2
    - @tauri-apps/api [NPM]: 2.0.0-alpha.8
    - @tauri-apps/cli [NPM]: 2.0.0-alpha.10

[-] App
    - build-type: build
    - CSP: unset
    - distDir: ../dist
    - devPath: http://localhost:1420/
    - framework: Svelte
    - bundler: Vite

Stack trace

No response

Additional context

No response