Fix unused field warning in cursor parsing

[psychon]

Rust nightly started to warn about an unused field while building examples:

warning: field `0` is never read
  --> x11rb/src/cursor/parse_cursor.rs:18:8
   |
18 |     Io(std::io::Error),
   |     -- ^^^^^^^^^^^^^^
   |     |
   |     field in this variant
   |
   = note: `#[warn(dead_code)]` on by default

The code from x11rb::cursor::parse_cursor is only called from x11rb::cursor::load_cursor(). This code completely ignores any errors and turns them into ParseError::InvalidValue. Thus, this warning is right.

[github-actions]

⚠️ [clippy] _{reported by reviewdog 🐶}

warning: unused import: `ErrorKind`
   --> x11rb/src/cursor/parse_cursor.rs:194:27
    |
194 |     use std::io::{Cursor, ErrorKind};
    |                           ^^^^^^^^^
    |
    = note: `#[warn(unused_imports)]` on by default

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (0fbfd89) 13.06% compared to head (64a515d) 13.06%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #915   +/-   ##
=======================================
  Coverage   13.06%   13.06%           
=======================================
  Files         190      190           
  Lines      136667   136663    -4     
=======================================
  Hits        17859    17859           
+ Misses     118808   118804    -4     

Flag	Coverage Δ
tests	13.06% <100.00%> (+<0.01%)	⬆️

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[notgull]

Thanks!