Fix the ExplicitSequenceFilenames rule breaking when updating single maps

[abcdefg30]

Reported by @PunkPun on Discord. Testcase is adding the following to any D2k map.yaml and running the ExplicitSequenceFilenames rule on that map.

Sequences:
	frigate:
		icon: DATA.R8
			Start: 4290
			Offset: -30,-24

Bleed will give:

Sequences:
	frigate:
		icon:
			Filename: DATA.R8
			Start: 4290
			Offset: -30,-24
		idle:
			Filename: frigate

And running it a second time will produce:

Sequences:
	frigate:
		icon:
			Filename: frigate
			Filename: DATA.R8
			Start: 4290
			Offset: -30,-24
		idle:
			Filename: frigate
			Filename: frigate

The expected result in both cases is:

Sequences:
	frigate:
		icon:
			Filename: DATA.R8
			Start: 4290
			Offset: -30,-24

Seems like #20580 both introduced Filename and the update rule, so it is save to say that sequence nodes that already have a Filename node are already processed and can be ignored.

The issue in the example happens because the mod sequence idle is already updated and the map only defined the extra icon sequence. The update rule was trying to update the already updated sequence from the mod code again instead of just the map sequence.

[PunkPun]

Are we sure this won't break the rule for updating mods? This doesn't queue changes like #20861 does

[abcdefg30]

I don't think we are processing the same node several times? The update rule doesn't behave properly when this node already exist anyway.

[PunkPun]

I meant in regards to reading defaults node. And it also seems this is completely unnecessary change. Update rules are not meant to be run on the same yaml twice. It's a waste of effort to try to make that a possibility.

[abcdefg30]

They are not meant to but might be. That is how this bug was detected after all. This PR would have been avoided if not for this very dismissive attitude.

[PunkPun]

In quite some cases, it's impossible or extremely hard to make rules rerun-proof. And since we won't make sure all are safe, I don't think it makes any sense to put in effort into making any of them rerun-safe.

And adding to that reruns are a user mistake, one that is very easily avoided.

I do want to make rules to require as little manual intervention as possible. Fleshing them out as much as possible, but accounting for user mistakes? I think is a bit much.

[abcdefg30]

The change has already been made. You are arguing to put more effort into this. I'm not saying we should go out of our way to build super complicated update rules, but the change is very easy here and good practice.

[PunkPun]

There is still effort left to put. We need to test whether this doesn't break mod updating

[abcdefg30]

a) Impossible, see the comment.
b) I already did regardless, and the automatic rules produce the same result as #20580.

[PunkPun]

ok I'm going to trust that

[PunkPun]

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