There are several BlockBackend functions which, in theory, cannot fail.
This patch makes them cope with the BlockDriverState pointer being NULL
by making them fall back to some default action like ignoring the value
in setters and returning the default in getters.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>