DirectoryBlob: Improve SetApploader

The code gets simpler by using IOFile instead of ReadFileToString.
Also, we now write -1 in all cases where loading fails.

Source/Core/DiscIO/DirectoryBlob.h

@@ -82,7 +82,7 @@ private:
   void SetTMDAndTicket();
 
   // Returns DOL address
-  u64 SetApploader(const std::string& apploader);
+  u64 SetApploader();
   // Returns FST address
   u64 SetDOL(u64 dol_address);