paycheck: Allow payloads with no operations.

Due to a fix to the delta generator (CL:246670) we may actually end up
with delta payloads that contain no operations (e.g. a delta from an
image to itself). This is a good thing and we want paycheck to not rule
out trivial deltas such as these.

BUG=chromium:453659
TEST=Empty delta verification passes

Change-Id: I461f48bba743a5b96b77aa3f55697ffc5cb8ea0e
Reviewed-on: https://chromium-review.googlesource.com/246673
Tested-by: Gilad Arnold <garnold@chromium.org>
Reviewed-by: Chris Sosa <sosa@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Commit-Queue: Gilad Arnold <garnold@chromium.org>
2 files changed