Assertion fails when passing `C:` as command line argument

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## Repro

Run the following command in this repository:

```sh
cargo run -- C:
```

## Expected result

Edit opens successfully with an untitled buffer.

## Actual result

Crashes with the following assertion error:

```
thread 'main' panicked at src\path.rs:12:5:
assertion failed: path.is_absolute()
stack backtrace:
0: std::panicking::begin_panic_handler
at /rustc/2805e1dc4c18ed4c84d161502c48da870c56f68a/library\std\src\panicking.rs:697
1: core::panicking::panic_fmt
at /rustc/2805e1dc4c18ed4c84d161502c48da870c56f68a/library\core\src\panicking.rs:75
2: core::panicking::panic
at /rustc/2805e1dc4c18ed4c84d161502c48da870c56f68a/library\core\src\panicking.rs:145
3: edit::path::normalize
at .\src\path.rs:12
4: edit::handle_args
at .\src\bin\edit\main.rs:253
5: edit::run
at .\src\bin\edit\main.rs:74
6: edit::main
at .\src\bin\edit\main.rs:56
7: core::ops::function::FnOnce::call_once >
at /rustc/2805e1dc4c18ed4c84d161502c48da870c56f68a\library\core\src\ops\function.rs:250
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
```

## Explanation

On Windows a drive letter path like `C:` is special. It is a relative path and it means the current working directory of the drive. If my understanding is correct, on Windows each drive has its current working directory.

This means

```rust
Path::new("C:").is_absolute()
```

returns `false` but

```rust
Path::new("C:\\foo").join("C:")
```

returns `C:`. This behavior causes the crash.

Start with the failing assertion in src/path.rs:12 and trace how src/bin/edit/main.rs handles the C: argument around handle_args. Reproduce the issue with cargo run -- C: on Windows, then verify that the command opens successfully with an untitled buffer without panicking.

Written by the indexing model from the issue text.