r14602: Fix another logic bug in new oplock handling. Just

r14602: Fix another logic bug in new oplock handling. Just
because lck->num_share_modes != 0 doesn't mean that
there *are* other valid share modes. They may be
all marked "UNUSED" or be deferred open entries.
In that case don't downgrade the granted oplock to
level2 needlessly - a client can have an exclusive
oplock in this case. The original code handled this
correctly in the lck->num_share_modes == 0 case but
not in the case where there were no valid share modes
but lck->num_share_modes != 0. I'll clean up my
Samba4 torture tester for this and commit it tomorrow.
Jeremy.
(This used to be commit 306061c93d9181262298516fefd83444f5a65ce5)