cros_generate_update_payload: Use patched kernel A if kernel B is empty.

When generating a delta payload, the source image may not have a normally
signed kernel in slot B if it's older. If that's the case, use the kernel in
slot A and patch it with the vblock from the stateful partition.

TEST=Tryjob, manual testing.

Change-Id: I047fc331f7bbbc08bb8e6024531d6473bb54aee6
Reviewed-by: Gabe Black <>
Commit-Queue: Gabe Black <>
Tested-by: Gabe Black <>
1 file changed