Fix PlayerMPD.rewind to start with the first song (#2323)

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):