Fix NPE when loadStructure fails

[TheDGOfficial]

Description

Fixes NPE when loadStructure fails.

The NPE is not from loadScript returning null or not from info.commandNames actually, it is from cfg.getFileName. So this PR makes fileName default to "" (does not matter anyway since loadStructure failed, we do not want to sync commands or such)

Maybe just continue on empty script info or null cfg but that may change behaviour. I've tested this and it correctly sends permission denied errors.

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Target Minecraft Versions: any
Requirements: none
Related Issues: #3804

[TPGamesNL]

IMO it would be better to make sure every method that returns one or more Configs can't return null values (as value or list element). Some methods already do this:

Skript/src/main/java/ch/njol/skript/ScriptLoader.java

Lines 823 to 825 in 885a4b6

	Config cfg = loadStructure(f);
	if (cfg != null)
	loadedFiles.add(cfg);

but not all:

Skript/src/main/java/ch/njol/skript/ScriptLoader.java

Lines 797 to 803 in 885a4b6

	List<Config> loadedFiles = new ArrayList<>(files.length);
	for (final File f : files) {
	assert f != null : Arrays.toString(files);
	loadedFiles.add(loadStructure(f));
	}
	return loadedFiles;

[TheDGOfficial]

Yes, that would be better. Looking now.

[TheDGOfficial]

I just added the null check to the method you've mentioned and the one that causes this error. Don't have time to look into all methods to find all ones that can return arrays/lists with null values though, so let me know if I've missed any.

[TPGamesNL]

You should look at the usages of ScriptLoader.loadStructure(File), since that's the method that's used everywhere (ScriptLoader, EffScriptFile and SkriptCommand).
PS I said it wrong in my last message, since a method returning a single Config should return null sometimes. I meant to say that all other methods using this should account for that, which they don't.

[TPGamesNL]

Closing as #3924 has been merged, fixing the same issues