Make sure CScript::GetSigOpCount(CScript &) is tested when called on non P2SH scripts.

Summary: This codepath is not tested at the moment.

Test Plan: Added test cases.

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1599