fix panic with lines on an error (#9967)

should close https://github.com/nushell/nushell/issues/9965

# Description
this PR implements the `todo!()` left in `lines`.

# User-Facing Changes
### before
```nushell
> open . | lines
thread 'main' panicked at 'not yet implemented', crates/nu-command/src/filters/lines.rs:248:35
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
```

### after
```nushell
> open . | lines
Error: nu:🐚:io_error

  × I/O error
  help: Is a directory (os error 21)
```

# Tests + Formatting
- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- ⚫ `toolkit test`
- ⚫ `toolkit test stdlib`

this PR adds the `lines_on_error` test to make sure this does not happen
again 😌

# After Submitting

crates/nu-command/src/filters/lines.rs

@@ -245,7 +245,7 @@ impl Iterator for RawStreamLinesAdapter {
                                 }
                             }
                         }
-                        Err(_) => todo!(),
+                        Err(err) => return Some(Err(err)),
                     }
                 } else {
                     self.inner_complete = true;

crates/nu-command/tests/commands/lines.rs

@@ -61,3 +61,11 @@ fn lines_mixed_line_endings() {
 
     assert_eq!(actual.out, "3");
 }
+
+#[cfg(not(windows))]
+#[test]
+fn lines_on_error() {
+    let actual = nu!("open . | lines");
+
+    assert!(actual.err.contains("Is a directory"));
+}