GameList: Add method to look up a cover image

src/frontend-common/game_list.h

@@ -108,6 +108,8 @@ public:
   void UpdateGameSettings(const std::string& filename, const std::string& game_code, const std::string& game_title,
                           const GameSettings::Entry& new_entry, bool save_to_list = true, bool save_to_user = true);
 
+  std::string GetCoverImagePathForEntry(const GameListEntry* entry);
+
 private:
   enum : u32
   {