SongLoader: move code to LoadFromDatabase()

Avoids the recursion in LoadFile().

src/SongLoader.hxx

@@ -70,6 +70,9 @@ public:
 	DetachedSong *LoadSong(const char *uri_utf8, Error &error) const;
 
 private:
+	gcc_nonnull_all
+	DetachedSong *LoadFromDatabase(const char *uri, Error &error) const;
+
 	gcc_nonnull_all
 	DetachedSong *LoadFile(const char *path_utf8, Error &error) const;
 };