notificationDaemon: Fix sound-file support
When commit 25bfe99e replaced the thin libcanberra wrapper with the (then) new MetaSoundPlayer API, it missed that the latter expects files as GFile instead of a file path.
When commit 25bfe99e replaced the thin libcanberra wrapper with the (then) new MetaSoundPlayer API, it missed that the latter expects files as GFile instead of a file path.