smbd: Avoid large reads beyond EOF

smbd: Avoid large reads beyond EOF

With unix extensions and oplocks=no mount.cifs from jessie reads beyond the
file end forever, and we are happy to return zeros....

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11878

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Wed Apr 27 23:57:56 CEST 2016 on sn-devel-144

(cherry picked from commit 10b0a8baa25fab70df8e6c5f0048ce0963211517)