Fix exceptions when selecting struct fields in tree view.

ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs

@@ -535,11 +535,13 @@ namespace ICSharpCode.Decompiler.CSharp
 			ITypeDefinition parentTypeDef = null;
 			syntaxTree = new SyntaxTree();
 			var decompileRun = new DecompileRun(settings) { CancellationToken = CancellationToken };
-			foreach (var entity in definitions)
-				RequiredNamespaceCollector.CollectNamespaces(entity, typeSystem, decompileRun.Namespaces);
 			foreach (var entity in definitions) {
 				if (entity.IsNil)
 					throw new ArgumentException("definitions contains null element");
+				RequiredNamespaceCollector.CollectNamespaces(entity, typeSystem, decompileRun.Namespaces);
+			}
+
+			foreach (var entity in definitions) {
 				switch (entity.Kind) {
 					case HandleKind.TypeDefinition:
 						ITypeDefinition typeDef = typeSystem.ResolveAsType(entity).GetDefinition();

ILSpy/Languages/CSharpLanguage.cs

@@ -228,11 +228,11 @@ namespace ICSharpCode.ILSpy
 		{
 			var members = new List<EntityHandle>();
 			foreach (var field in type.Fields) {
-				if (field.IsStatic == isStatic)
+				if (!field.MetadataToken.IsNil && field.IsStatic == isStatic)
 					members.Add(field.MetadataToken);
 			}
 			foreach (var ctor in type.Methods) {
-				if (ctor.IsConstructor && ctor.IsStatic == isStatic)
+				if (!ctor.MetadataToken.IsNil && ctor.IsConstructor && ctor.IsStatic == isStatic)
 					members.Add(ctor.MetadataToken);
 			}