Fix #1372: XML security attributes are not added to the output.

ICSharpCode.Decompiler/TypeSystem/Implementation/AttributeListBuilder.cs

@@ -245,16 +245,17 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			} else {
 				// for backward compatibility with .NET 1.0: XML-encoded attribute
 				reader.Reset();
-				ReadXmlSecurityAttribute(ref reader, securityAction);
+				Add(ReadXmlSecurityAttribute(ref reader, securityAction));
 			}
 		}
 
-		private void ReadXmlSecurityAttribute(ref SRM.BlobReader reader, CustomAttributeTypedArgument<IType> securityAction)
+		private IAttribute ReadXmlSecurityAttribute(ref SRM.BlobReader reader, CustomAttributeTypedArgument<IType> securityAction)
 		{
 			string xml = reader.ReadUTF16(reader.RemainingBytes);
 			var b = new AttributeBuilder(module, KnownAttribute.PermissionSet);
 			b.AddFixedArg(securityAction);
 			b.AddNamedArg("XML", KnownTypeCode.String, xml);
+			return b.Build();
 		}
 
 		private IAttribute ReadBinarySecurityAttribute(ref SRM.BlobReader reader, CustomAttributeTypedArgument<IType> securityAction)

ICSharpCode.Decompiler/TypeSystem/Implementation/KnownAttributes.cs

@@ -144,7 +144,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 			// Marshalling attributes:
 			new TopLevelTypeName("System.Runtime.InteropServices", nameof(MarshalAsAttribute)),
 			// Security attributes:
-			new TopLevelTypeName("System.Security", "PermissionSetAttribute"),
+			new TopLevelTypeName("System.Security.Permissions", "PermissionSetAttribute"),
 		};
 
 		public static ref readonly TopLevelTypeName GetTypeName(this KnownAttribute attr)