G_ABORT_ON_FAILED_ASSUME is true, inline_check_non_fatal called assertion_fail() and then had a throw NonFatalCheckError that was never reachable, because assertion_fail() either aborts or throws and never returns.
Refactored inline_check_non_fatal to use if constexpr (G_ABORT_ON_FAILED_ASSUME) { assertion_fail(...) } else { throw NonFatalCheckError(...) } branch, removing the unreachable throw