DDF: Fix NULL pointer dereference in validate_geometry_ddf()

DDF: Fix NULL pointer dereference in validate_geometry_ddf()

A relatively recent patch added a call to validate_geometry() in
Manage_add() that has level=LEVEL_CONTAINER and chunk=NULL.

This causes some ddf tests to segfault which aborts the test suite.

To fix this, avoid dereferencing chunk when the level is
LEVEL_CONTAINER or LEVEL_NONE.

Fixes: 1f5d54a06df0 ("Manage: Call validate_geometry when adding drive to external container")
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Acked-by: Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>
Signed-off-by: Jes Sorensen <jes@trained-monkey.org>