Fix an off by one error in the peephole optimizer when checking for unreachable code beyond a return.
Do a bounds check within find_op so it can return before going past the end as a safety measure.
7db3c48833 (diff-a33329ae6ae0bb295d742f0caf93c137)
introduced this off by one error while fixing another one nearby.
This bug was shipped in all Python 3.6 and 3.7 releases.
The included unittest won't fail unless you do a clang msan build.
Miscellaneous source files for the main Python shared library