Don't clear is_sorted unconditionally on OPENSSL_sk_insert()

Don't clear is_sorted unconditionally on OPENSSL_sk_insert()

If we have a comparison function, and the array was sorted,
check to see if we are inserting in the correct location.
if so do not clear is_sorted.

This allows for element locations found with OPENSSL_sk_find_ex
to be used to insert elements in the correct location and preserve
the sorting order without the need to sort the stack again.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <ppzgs1@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/28533)