Better error message for invalid custom scheme name on webkit

[ottomated]

Is your feature request related to a problem? Please describe.

When registering an invalid scheme like so .register_asynchronous_uri_scheme_protocol("in_valid", ...), the error (on macos) is:

thread 'main' panicked at ~/.cargo/registry/src/index.crates.io-6f17d22bba15001f/wry-0.40.1/src/wkwebview/mod.rs:403:18:
Uncaught exception <NSException: 0x149f0c280>
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
libc++abi: terminating due to uncaught foreign exception

Describe the solution you'd like
Either the scheme name should be validated on the Rust end beforehand or the error from webkit should be handled better.

Additional context
Tested on tauri 2.0.0-beta

[pewsheen]

Thanks for the report!
Currently, the objc crate we are using can't tell which NSException it is, so we don't know if the thrown exception is either the scheme name is invalid, or it's already been registered. Checking the name before using it looks more promising for now.

[ottomated]

Honestly, even The schema "in_valid" is invalid or already registered would be enough in my opinion. The issue right now is that it doesn't point to scheme registration at all