pNFS/filelayout: fix cheking if a layout is striped

pNFS/filelayout: fix cheking if a layout is striped

A layout can still be striped with num_fh = 1 as it is perfectly possible
that both MDS and DSs can handle the same filehandle. Hence check according
to stripe_count > 1, which is the correct check to begin with.

We should not be called with flseg->dsaddr = NULL, but if for some reason
we do, return our best guess with is flseg->num_fh > 1.

Fixes: a6b9d2fa0024 ("pNFS/filelayout: Fix coalescing test for single DS")
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Anna Schumaker <anna.schumaker@hammerspace.com>