Minor fixes in the writer

Author: liuzicheng1987

include/rfl/cbor/Writer.hpp

@@ -94,7 +94,7 @@ class Writer {
   template <class T>
   OutputVarType add_value_to_object(const std::string& _name, const T& _var,
                                     OutputObjectType* _parent) const noexcept {
-    cbor_encode_text_string(_parent, _name.c_str(), _name.size());
+    cbor_encode_text_string(_parent->encoder_, _name.c_str(), _name.size());
     return new_value(_var, _parent->encoder_);
   }
 
@@ -105,7 +105,7 @@ class Writer {
 
   OutputVarType add_null_to_object(const std::string& _name,
                                    OutputObjectType* _parent) const noexcept {
-    cbor_encode_text_string(_parent, _name.c_str(), _name.size());
+    cbor_encode_text_string(_parent->encoder_, _name.c_str(), _name.size());
     cbor_encode_null(_parent->encoder_);
     return OutputVarType{};
   }