Skip corrupted .acf files in Steam library

[HebaruSan]

Problem

After the v1.35.0 release, several users reported an exception at launch:

Unhandled Exception: ValveKeyValue.KeyValueException: Found end of file when another token type was expected. ---> System.InvalidOperationException: Attempted to finalize object while in state InObjectBetweenKeyAndValue.
   at ValveKeyValue.Deserialization.KV1TextReader.FinalizeCurrentObject(Boolean explicit)
   at ValveKeyValue.Deserialization.KV1TextReader.FinalizeDocument()
   at ValveKeyValue.Deserialization.KV1TextReader.ReadObject()
   --- End of inner exception stack trace ---
   at ValveKeyValue.Deserialization.KV1TextReader.ReadObject()
   at ValveKeyValue.KVSerializer.Deserialize(Stream stream, KVSerializerOptions options)
   at CKAN.SteamLibrary.<>c__DisplayClass3_0.<LibraryPathGames>b__0(String acfFile)
   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
   at System.Linq.Enumerable.<SelectManyIterator>d__17`2.MoveNext()
   at System.Linq.Enumerable.<ConcatIterator>d__59`1.MoveNext()
   at System.Linq.Buffer`1..ctor(IEnumerable`1 source)
   at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
   at CKAN.SteamLibrary..ctor()
   at CKAN.GameInstanceManager..ctor(IUser user, IConfiguration configuration)
   at CKAN.CmdLine.MainClass.Execute(GameInstanceManager manager, CommonOptions opts, String[] args)
   at CKAN.CmdLine.MainClass.Main(String[] args)

Cause

@Halbann reports:

I stepped through the code and found it was just one acf file responsible that was just a few hundred null bytes with no text. I don't own the game it was for anymore. I deleted the file and CKAN worked fine after that.

Side note: the file was last modified in 2018 so it had obviously been there corrupted for some time without Steam cleaning it up.

Apparently Steam sometimes corrupts one of the important files in its database and then just leaves it there (in addition to leaving a bunch of empty folders after it disables a DLC, see #4002). (Windows may be partly responsible, since this all-null file strongly is strongly reminiscent of #4078, which our code would never cause if the OS ran it as written.) Once this happens, KeyValueValue.KVSerializer.Deserialize throws an exception when asked to read such a file.

Changes

Now if Deserialize throws an exception, we log a warning and continue with the other .acf files.

We will continue to investigate this as other affected users report back, in case they are experiencing the same issue with different causes, but for now this is one definite problem we can address.

Fixes #4197.

[kretze]

Problem found

File deleted. CKAN starts without errors

---

Steam libraries were repeatedly transferred from PC / HDD to newer ones and integrated again.
There must have been some old leftovers there.