Exempt ignored PA-TNC attributes from error handling

src/libimcv/pa_tnc/pa_tnc_msg.c

@@ -225,9 +225,16 @@ METHOD(pa_tnc_msg_t, process, status_t,
 		attr = imcv_pa_tnc_attributes->create(imcv_pa_tnc_attributes,
 							reader, FALSE, &offset, this->encoding, &error);
 		if (!attr)
+		{
+			if (error)
 			{
 				goto err;
 			}
+			else
+			{
+				continue;
+			}
+		}
 		attr_value = attr->get_value(attr);
 		attr_type  = attr->get_type(attr);