Do not re-run image comparer if inputs have not changed

[DRuggeri]

Very quick and small fix to let the image comparer step aside if the inputs have not changed. This avoids frontend redownloading/rendering of unchanged data (most noticeable on mobile, at least for me)

[rgthree]

Normally nodes don't run if the graph before hand hasn't changed, so this isn't really doing anything that I can see as far as inputs changing goes. But I could see this improving if the inputs did change.. but the image data being passed in didn't change.

Is that what you're seeing?

[DRuggeri]

Well, it's actually tough to say. I started down this path because I noticed unexpected pauses while the comparer was running and images were downloading, even when running a workflow with several image compare nodes coming from steps that had not changed. This was surprising, so I was suspecting that the comparison run/download of both images was being repeated unnecessarily.

However, it's possible that what is feeding the image comparer (a node that overlays text on the two images) is propagating a "change" even without changes, so I was expecting the SHA comparison could help. This occurs both in nodes view and app mode. In practice, it doesn't seem to stop the node from processing... but it felt correct to keep so thought I would share for feedback.