A few fixes for .NET Core and Reactor v6.9.8.0

[JBou]

This PR fixes a few problems I encountered using Reactor 6.9.8.0

• Fixed decompressing resources when Brotli compression was used
• Fixed .NET Core Method Decryption for DNR v6.9.8.0
• Fixed NPE in AssemblyResolver
• Fix NPE in StringDecrypter

Thanks a lot for this useful tool and your hard work!