vboot/sign_official_build: Skip re-signing empty miniOS partitions

Reasons that miniOS partitions might be empty is that the feature is not
enabled yet, but the partitions exist as it's using the newer

TEST=# run tests
Signed-off-by: Jae Hoon Kim <kimjae@chromium.org>

Change-Id: I2a6b68240428ab2f01394230840ff116c720b3df
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/3145770
Tested-by: Jae Hoon Kim <kimjae@chromium.org>
Auto-Submit: Jae Hoon Kim <kimjae@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Commit-Queue: Julius Werner <jwerner@chromium.org>
1 file changed