Don't store empty chat_type.

telegram-bot-api/Client.cpp

@@ -1941,8 +1941,10 @@ class Client::JsonInlineQuery : public Jsonable {
             return "";
         }
       }();
+      if (chat_type[0] != '\0') {
         object("chat_type", chat_type);
       }
+    }
     object("query", query_);
     object("offset", offset_);
   }