Fixed decompiling empty async methods.

Fixes #417 #446 #479

ICSharpCode.Decompiler/ILAst/StateRange.cs

@@ -212,6 +212,9 @@ namespace ICSharpCode.Decompiler.ILAst
 					case ILCode.Br:
 					case ILCode.Leave:
 						ranges[(ILLabel)expr.Operand].UnionWith(nodeRange);
+						if (i == bodyLength - 1)
+							// no states
+							goto default;
 						break;
 					case ILCode.Brtrue:
 						{

ICSharpCode.Decompiler/Tests/Async.cs

@@ -25,6 +25,10 @@ using System.Threading.Tasks;
 
 public class Async
 {
+	public async void EmptyAsyncMethod()
+	{
+	}
+
 	public async void SimpleVoidMethod()
 	{
 		Console.WriteLine("Before");