Fix #1518: Missing Detach()-call in AST manipulation.

ICSharpCode.Decompiler/CSharp/CallBuilder.cs

@@ -334,7 +334,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				// settings.AlwaysCastTargetsOfExplicitInterfaceImplementationCalls == true is used in Windows Forms' InitializeComponent methods.
 				if (method.IsExplicitInterfaceImplementation && (target.Expression is ThisReferenceExpression || settings.AlwaysCastTargetsOfExplicitInterfaceImplementationCalls)) {
 					var interfaceMember = method.ExplicitlyImplementedInterfaceMembers.First();
-					var castExpression = new CastExpression(expressionBuilder.ConvertType(interfaceMember.DeclaringType), target.Expression);
+					var castExpression = new CastExpression(expressionBuilder.ConvertType(interfaceMember.DeclaringType), target.Expression.Detach());
 					methodName = interfaceMember.Name;
 					targetExpr = new MemberReferenceExpression(castExpression, methodName);
 					typeArgumentList = ((MemberReferenceExpression)targetExpr).TypeArguments;