`--show-source` used together with isort and line continuation characters panics

[squiddy]

from module import member1, \
     member2

❯ RUST_BACKTRACE=1 cargo run test.py --show-source --select I --no-cache
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Line index out of bounds: line index 3, Rope/RopeSlice line count 2', /home/squiddy/.cargo/registry/src/github.com-1ecc6299db9ec823/ropey-1.5.0/src/rope.rs:764:41

<snip>

   4: ropey::rope::Rope::line_to_char
             at /home/squiddy/.cargo/registry/src/github.com-1ecc6299db9ec823/ropey-1.5.0/src/rope.rs:764:9
   5: ruff::source_code_locator::SourceCodeLocator::slice_source_code_range
             at ./src/source_code_locator.rs:43:19
   6: ruff::message::Source::from_check
             at ./src/message.rs:58:22
   7: ruff::linter::lint::{{closure}}
             at ./src/linter.rs:353:26

<snip>

---

When running cargo run resources/test/fixtures/isort/* --show-source --select I I can see some seemingly wrong check locations. The source code slices are cut off, e.g.

resources/test/fixtures/isort/combine_as_imports.py:1:1: I001 Import block is un-sorted or un-formatted
  |
1 | / from module import Class as C
2 | | from module import CONSTANT
3 | | from module import function
4 | | from module import function as f