cgpt: do not show length of 1 for undefined partitions
cgpt: do not show length of 1 for undefined partitions

If a partition isn't "defined", then don't declare its size as 1.

BUG=chromium:236941
TEST=`cbuildbot {x86,amd64,arm}-generic-full` pass
TEST=`cgpt show -i 100 -s chromiumos_image.bin` shows 0
BRANCH=none

Change-Id: I538546b6b37a9137958d6f926a58753cf52c946a
Reviewed-on: https://gerrit.chromium.org/gerrit/50074
Reviewed-by: Bill Richardson <129945214b1d548d8e49b6c29c43094f8c78057f@chromium.org>
Commit-Queue: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@chromium.org>
Tested-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@chromium.org>

coreboot/vboot,coreboot/vboot,acorn-marvell/vboot_reference,coreboot/vboot,geekboxzone/mmallow_external_vboot_reference,acorn-marvell/vboot_reference,geekboxzone/mmallow_external_vboot_reference,geekboxzone/mmallow_external_vboot_reference,ccaapton/vboot_reference,ccaapton/vboot_reference,acorn-marvell/vboot_reference,coreboot/vboot,geekboxzone/mmallow_external_vboot_reference,coreboot/vboot,acorn-marvell/vboot_reference,ccaapton/vboot_reference,ccaapton/vboot_reference,geekboxzone/mmallow_external_vboot_reference