Adds one extra test to the ABFS close logic, to explicitly
verify that the close sequence of FilterOutputStream is
not going to fail.
This is just a due-diligence patch, but it helps ensure
that no regressions creep in in future.
Contributed by Steve Loughran.
Change-Id: Ifd33a8c322d32513411405b15f50a1aebcfa6e48
6a859d33aa