handle the situation where the user requests a non-zero amount
of data but has a zero-size fileview. My instrinct would have been
to return an error code, but according to the test that I used
it should be MPI_SUCCESS and zero bytes. It is definitely better
than segfaulting :-)
THis makes another test from the IBM testsuite pass.
Signed-off-by: Edgar Gabriel <egabriel@central.uh.edu>