search provider: Don't try to process if ID is invalid

[City-busz]

It causes a panic if invalid ID is sent via D-Bus.

$ gdbus call -e -d com.github.finefindus.eyedropper.SearchProvider -o /com/github/finefindus/eyedropper/SearchProvider -m org.gnome.Shell.SearchProvider2.GetResultMetas '["invalid"]'

$ gdbus call -e -d com.github.finefindus.eyedropper.SearchProvider -o /com/github/finefindus/eyedropper/SearchProvider -m org.gnome.Shell.SearchProvider2.ActivateResult "invalid" "[]" 0

Which causes the following panic:

thread 'main' panicked at src/application.rs:266:58:
Failed to parse identifier color: BoolError { message: "Can't parse RGBA", filename: "/usr/src/debug/eyedropper/build/cargo-home/registry/src/index.crates.io-1949cf8c6b5b557f/gdk4-0.9.6/src/rgba.rs", function: "gdk4::rgba::<impl gdk4::auto::rgba::RGBA>::parse::{{closure}}", line: 207 }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

thread 'zbus::Connection executor' panicked at /usr/src/debug/eyedropper/build/cargo-home/registry/src/index.crates.io-1949cf8c6b5b557f/search-provider-0.11.0/src/search_provider.rs:157:39:
called `Result::unwrap()` on an `Err` value: Canceled

thread 'main' panicked at src/application.rs:247:55:
called `Result::unwrap()` on an `Err` value: BoolError { message: "Can't parse RGBA", filename: "/usr/src/debug/eyedropper/build/cargo-home/registry/src/index.crates.io-1949cf8c6b5b557f/gdk4-0.9.6/src/rgba.rs", function: "gdk4::rgba::<impl gdk4::auto::rgba::RGBA>::parse::{{closure}}", line: 207 }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

This change fixes that.

[FineFindus]

I'm not too happy with this, as it's handling an invariant, that is already guaranteed by the D-Bus interface.

[FineFindus]

Thanks!