A transaction is valid if nothing in the combined script triggers
failure and the top stack item is true (non-zero).
However, P2WPKH and P2WSH scriptPubkeys are two data pushes of witness versions and witness programs with empty scriptsigs spending them. From a pre-segwit client perspective, stack is ending with data pushes which are non-true? If so how do legacy clients evaluate segwit spends true?