Fix PlayerMPD.prev/next() when stopped

* Avoid MPD-related crashes during all prev/next() calls.
* Explicitly handle prev() in stopped state
* Explicitly handle next() in stopped state
* Explicitly handle next() when reaching the end of the playlist:
  jukebox-daemon will now stop playing by default (similar to v2).
  It can also be configured to restart the playlist instead by setting
  the new config option `playermpd.end_of_playlist_next_action: rewind`.

Fixes MiczFlor#2294

resources/default-settings/jukebox.default.yaml

@@ -87,6 +87,8 @@ playermpd:
     update_on_startup: true
     check_user_rights: true
   mpd_conf: ~/.config/mpd/mpd.conf
+  # Must be one of: 'stop', 'rewind':
+  end_of_playlist_next_action: stop
 rpc:
   tcp_port: 5555
   websocket_port: 5556

src/jukebox/components/playermpd/__init__.py

@@ -156,6 +156,11 @@ def __init__(self):
         self.second_swipe_action = None
         self.decode_2nd_swipe_option()
 
+        self.end_of_playlist_next_action_dict = {'rewind': self.rewind,
+                                                 'stop': self.stop}
+        self.end_of_playlist_next_action = None
+        self.decode_end_of_playlist_next_action()
+
         self.mpd_client = mpd.MPDClient()
         self.coverart_cache_manager = CoverartCacheManager()
 
@@ -231,6 +236,14 @@ def decode_2nd_swipe_option(self):
                                                          custom_action['args'],
                                                          custom_action['kwargs'])
 
+    def decode_end_of_playlist_next_action(self):
+        end_of_playlist_next_action = cfg.setndefault('playermpd', 'end_of_playlist_next_action', value='stop').lower()
+        if end_of_playlist_next_action in self.end_of_playlist_next_action_dict:
+            self.end_of_playlist_next_action = self.end_of_playlist_next_action_dict[end_of_playlist_next_action]
+        else:
+            logger.error(f'Config mpd.end_of_playlist_next_action must be one of '
+                         f'{self.end_of_playlist_next_action.keys()}. Ignore setting.')
+
     def mpd_retry_with_mutex(self, mpd_cmd, *args):
         """
         This method adds thread saftey for acceses to mpd via a mutex lock,
@@ -327,15 +340,37 @@ def pause(self, state: int = 1):
     @plugs.tag
     def prev(self):
         logger.debug("Prev")
-        with self.mpd_lock:
-            self.mpd_client.previous()
+        if self.mpd_status['state'] == 'stop':
+            logger.debug('Player is stopped, rewinding instead')
+            return self.rewind()
+        try:
+            with self.mpd_lock:
+                self.mpd_client.previous()
+        except mpd.base.CommandError:
+            # This shouldn't happen in reality, but we still catch
+            # this error to avoid crashing the player thread:
+            logger.warning('Failed to go to previous song, ignoring')
 
     @plugs.tag
     def next(self):
         """Play next track in current playlist"""
         logger.debug("Next")
-        with self.mpd_lock:
-            self.mpd_client.next()
+        if self.mpd_status['state'] == 'stop':
+            logger.debug('Player is stopped, rewinding instead')
+            return self.rewind()
+        playlist_len = int(self.mpd_status.get('playlistlength', -1))
+        current_pos = int(self.mpd_status.get('pos', 0))
+        if current_pos == playlist_len - 1:
+            logger.debug(f'next() called during last song ({current_pos}) of '
+                         f'playlist (len={playlist_len}), running end_of_playlist_next_action.')
+            return self.end_of_playlist_next_action()
+        try:
+            with self.mpd_lock:
+                self.mpd_client.next()
+        except mpd.base.CommandError:
+            # This shouldn't happen in reality, but we still catch
+            # this error to avoid crashing the player thread:
+            logger.warning('Failed to go to next song, ignoring')
 
     @plugs.tag
     def seek(self, new_time):