[3.12] gh-105375: Improve error handling in the sys extension module (GH-105611) (#105665)

In _PySys_AddXOptionWithError() and sys_add_xoption(),
bail on first error to prevent exceptions from possibly being
overwritten.
(cherry picked from commit 41cddc2e93a285b81fa30ac542b088bd9d0112e9)

Co-authored-by: Erlend E. Aasland <erlend.aasland@protonmail.com>