Android: Don't hold gameFileCache lock during updateAdditionalMetadata

It seems like we spend a lot of the game list scanning time in
updateAdditionalMetadata, which I suppose makes sense considering
how many different files that function attempts to open.

With the addition of just one little atomic operation, we can make
it safe to call updateAdditionalMetadata without holding a lock.

Source/Core/UICommon/GameFileCache.cpp

@@ -4,6 +4,7 @@
 #include "UICommon/GameFileCache.h"
 
 #include <algorithm>
+#include <atomic>
 #include <cstddef>
 #include <functional>
 #include <list>
@@ -202,7 +203,7 @@ bool GameFileCache::UpdateAdditionalMetadata(std::shared_ptr<GameFile>* game_fil
   if (custom_cover_changed)
     copy->CustomCoverCommit();
 
-  *game_file = std::move(copy);
+  std::atomic_store(game_file, std::move(copy));
 
   return true;
 }