Safely close database connections and delete backends

Also fix NewClosure leak caused by disconnected object signals

src/device/gpodloader.cpp

@@ -102,6 +102,8 @@ Itdb_iTunesDB *GPodLoader::TryLoad() {
   // Add the songs we've just loaded
   backend_->AddOrUpdateSongs(songs);
 
+  backend_->Close();
+
   return db;
 
 }