bpo-41687: Fix error handling in Solaris sendfile implementation (GH-22128)


I just realized that my recent PR with sendfile on Solaris ([PR 22040](https://github.com/python/cpython/pull/22040)) has broken error handling.

Sorry for that, this simple followup fixes that.

Automerge-Triggered-By: @1st1
(cherry picked from commit fa8c9e70104b0aef966a518eb3a80a4881906ae0)

Co-authored-by: Jakub KulĂ­k <Kulikjak@gmail.com>
1 file changed