Test case for pss signature problem.

* rsa-pss-sign-tr-test.c (test_main): Add test case
contributed by Daiki Ueno. Problem originally found by oss-fuzz,
see https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=2132.
That problem report is currently embargoed, but will hopefully be
public in a month or two.