[3.14] gh-140594: Fix an out of bounds read when feeding NUL byte to PyOS_StdioReadline() (GH-140910) (#145852)

gh-140594: Fix an out of bounds read when feeding NUL byte to PyOS_StdioReadline() (GH-140910)
(cherry picked from commit 86a0756234df7ce42fa4731c91067cb7f2e244d5)

Co-authored-by: Shamil <ashm.tech@proton.me>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
Co-authored-by: Victor Stinner <vstinner@python.org>