Fix null reference exception in swinfo transformer

[HebaruSan]

Problem

QuestariaAerospace had an inflation error in its previous release, see KSP-CKAN/KSP2-NetKAN#144:

1780 [1] FATAL CKAN.NetKAN.Program (null) - Object reference not set to an instance of an object.
1847 [1] FATAL CKAN.NetKAN.Program (null) -    at CKAN.NetKAN.Transformers.SpaceWarpInfoTransformer.<Transform>d__3.MoveNext()
   at System.Linq.Enumerable.<SelectManyIterator>d__17`2.MoveNext()
   at System.Linq.Buffer`1..ctor(IEnumerable`1 source)
   at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
   at CKAN.NetKAN.Transformers.NetkanTransformer.Transform(Metadata metadata, TransformOptions opts)
   at CKAN.NetKAN.Processors.Inflator.<>c__DisplayClass1_0.<Inflate>b__0(Metadata netkan)
   at System.Linq.Enumerable.<SelectManyIterator>d__17`2.MoveNext()
   at System.Linq.Lookup`2.Create[TSource](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer)
   at System.Linq.GroupedEnumerable`3.GetEnumerator()
   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at CKAN.NetKAN.Processors.Inflator.Inflate(String filename, Metadata[] netkans, TransformOptions opts)
   at CKAN.NetKAN.Program.Main(String[] args)

Cause

The ksp2_version property was missing. This was due to an issue with KSP2UnityTools, but this is supposed to be allowed.

Changes

• Now we access this property's properties with the ?. null coalescing operator so it won't throw if null
• While looking into this, I had doubts about how short circuiting with || would affect parsing of min and max versions, so now we parse both in separate statements.