Properly Populate Player Index

The player_index field in question is ultimately what gets used to determine which ranks get displayed in the leaderboards chart, and because this was missing the chart was simply displaying the top four results no matter what.

Source/Core/Core/AchievementManager.cpp

@@ -804,6 +804,8 @@ void AchievementManager::LeaderboardEntriesCallback(int result, const char* erro
     map_entry.username.assign(response_entry.user);
     memcpy(map_entry.score.data(), response_entry.display, FORMAT_SIZE);
     map_entry.rank = response_entry.rank;
+    if (ix == list->user_index)
+      leaderboard.player_index = response_entry.rank;
   }
   AchievementManager::GetInstance().m_update_callback({.leaderboards = {*leaderboard_id}});
 }