player_thread: clear player.queued after failure

When pc.next_song is reset due to a decoder failure, also reset the
player.queued flag.  player.queued must not be true when there is no
pc.next_song.

src/player_thread.c

@@ -142,6 +142,7 @@ player_wait_for_decoder(struct player *player)
 		pc.errored_song = dc.next_song;
 		pc.error = PLAYER_ERROR_FILE;
 		pc.next_song = NULL;
+		player->queued = false;
 		return false;
 	}