Fix Netkan swinfo transformer null list error

[HebaruSan]

Problem

KSP-CKAN/KSP2-NetKAN#75

Cause

If a module has no depends relationships, then mod.depends is null here, and .Select doesn't work:

CKAN/Netkan/Transformers/SpaceWarpInfoTransformer.cs

Lines 87 to 89 in 83b6e7d

	var moduleDeps = mod.depends.Select(r => (r as ModuleRelationshipDescriptor)?.name)
	.Where(ident => ident != null)
	.ToHashSet();

This problem was masked by all previous mods with swinfo.json files having a dependency on SpaceWarp.

Changes

Now if CkanModule.depends is null, we substitute the empty sequence.

Will self-review so that pull request can proceed.