[BUG] Missing test for memory corruption in range window queries on null timestamps

#7568 fixed the null-bounds calculation for time range window functions, for cases where the timestamp column might contain nulls. No tests were added as part of the fix, because the crash is elusive. There already are tests for grouped time-range rolling windows that exercise this code path, but do not crash on account of the out-of-bounds access.

It would be good to add a test that reproduces the error condition.