testsuite: Use safe FFI call in T5611
The original issue, #5611, was concerned with safe calls. However, the test inexplicably used an unsafe call. Fix this.
However, I also add a T5611a testcase exercising the unsafe call behavior.
The original issue, #5611, was concerned with safe calls. However, the test inexplicably used an unsafe call. Fix this.
However, I also add a T5611a testcase exercising the unsafe call behavior.