Migrate the fix for 6892 into reader itself

No functional change here; this migrates the fix ensuring that history
items are available in the builtin interactive read command into the
reader itself, in preparation for removing reader_get_history().

src/reader.cpp

@@ -2568,6 +2568,7 @@ static std::shared_ptr<reader_data_t> reader_push_ret(parser_t &parser,
                                                       const wcstring &history_name,
                                                       reader_config_t &&conf) {
     std::shared_ptr<history_t> hist = history_t::with_name(history_name);
+    hist->resolve_pending(); // see #6892
     auto data = std::make_shared<reader_data_t>(parser.shared(), hist, std::move(conf));
     reader_data_stack.push_back(data);
     data->command_line_changed(&data->command_line);