implemented RegisterRequest handler

src/network/tcp-chat-protocol/v1.c

@@ -56,8 +56,8 @@ Result(void) RegisterRequest_tryConstruct(RegisterRequest *ptr, PacketHeader* he
     _PacketHeader_construct(RegisterRequest);
 
     try_assert(username.size >= USERNAME_SIZE_MIN && username.size <= USERNAME_SIZE_MAX);
-    ptr->username_size = username.size;
     memcpy(ptr->username, username.data, username.size);
+    ptr->username[username.size] = 0;
 
     try_assert(token.size == sizeof(ptr->token));
     memcpy(ptr->token, token.data, token.size);