Merge #9555: [test] Avoid reading a potentially uninitialized variable in tx_invalid-test (transaction_tests.cpp)

Summary:
backport PR9555 https://github.com/bitcoin/bitcoin/pull/9555/files
8455e36 [test] Avoid reading a potentially uninitialized variable in tx_invalid-test (practicalswift)

Tree-SHA512: 1064cdd5c9e4612a05397a5880535d93dbb18dec4897b4bbda9e6ad78d30f4c72303e4d23159398f1b33545ff5819e739e374d7cde757e402b26c355268a2319

Test Plan: make check

Reviewers: jasonbcox, Fabien, #bitcoin_abc, deadalnix

Reviewed By: jasonbcox, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D2986