Fix PlayerMPD.rewind to start with the first song

rewind() is documented to jump to the first song of the playlist.
Instead, it jumped to the second song as SONGPOS in
MPDClient.play(SONGPOS) is zero-indexed [1], so mpd.play(1) started
the second song.

[1] https://mpd.readthedocs.io/en/latest/protocol.html#the-queue
"The position is a 0-based index"

Related: #2294

src/jukebox/components/playermpd/__init__.py

@@ -350,7 +350,7 @@ def rewind(self):
         Note: Will not re-read folder config, but leave settings untouched"""
         logger.debug("Rewind")
         with self.mpd_lock:
-            self.mpd_client.play(1)
+            self.mpd_client.play(0)
 
     @plugs.tag
     def replay(self):