Fix __lltrace__ debug feature if the stdout encoding is not UTF-8.

If the stdout encoding is not UTF-8, the first call to
lltrace_resume_frame() indirectly sets lltrace to 0 when calling
unicode_check_encoding_errors() which calls
encodings.search_function().
(cherry picked from commit 5695c0e0)

Co-authored-by: Victor Stinner <vstinner@python.org>