[PATCH 2/2] sadump: Perform explicit zero page filtering.

Currently, crash utility faces different behaviors on reading zero
pages that are filtered out on the kdump-compressed format originating
from kdump ELF and from sadump formats: the former succeeds in reading
zero pages but the latter fails. This is a design bug. To fix this
issue, perform zero pages filtering explicitly if some pages are
filtered out.

Signed-off-by: Takao Indoh <indou.takao@jp.fujitsu.com>
Signed-off-by: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>