[TypeSystem] GetClassTypeReference: Fixed CurrentAssembly == null

case.

ICSharpCode.NRefactory/TypeSystem/Implementation/GetClassTypeReference.cs

@@ -100,7 +100,7 @@ namespace ICSharpCode.NRefactory.TypeSystem.Implementation
 				}
 				if (type == null) {
 					var compilation = context.Compilation;
-					foreach (var asm in new[] { context.CurrentAssembly }.Concat(compilation.Assemblies)) {
+					foreach (var asm in (context.CurrentAssembly != null ? new[] { context.CurrentAssembly }.Concat(compilation.Assemblies) : compilation.Assemblies)) {
 						type = asm.GetTypeDefinition(fullTypeName);
 						if (type != null)
 							break;