ttstoy: make tts join behave as a summon

Connect to the caller's voice channel when the bot is not in voice, and
move to the caller's channel if the bot is currently in a different one
(via Player.move_to). Previously it only connected when the bot had no
voice state, so it would not follow the user between channels.

ttstoy/ttstoy.py

@@ -2434,12 +2434,21 @@ class TtsToy(Cog):
             # Check if user is in a VC - we'll play there if so, but it's not required
             user_in_vc = ctx.author.voice and ctx.author.voice.channel
 
-            if user_in_vc and not ctx.guild.me.voice:
-                # Connect via the shared Lavalink client (owned by the YTAudio cog).
+            if user_in_vc:
+                target_channel = ctx.author.voice.channel
+                me_voice = ctx.guild.me.voice
+                # Summon: connect if not in voice, or move if in a different channel.
+                if me_voice is None or me_voice.channel is None:
                     try:
-                    await lavalink.connect(ctx.author.voice.channel)
+                        await lavalink.connect(target_channel)
                     except Exception:
                         log.exception("[TTS] Failed to connect to voice channel via Lavalink.")
+                elif me_voice.channel.id != target_channel.id:
+                    try:
+                        player = lavalink.get_player(ctx.guild.id)
+                        await player.move_to(target_channel)
+                    except Exception:
+                        log.exception("[TTS] Failed to move to the user's voice channel.")
 
             mode = await self._get_tts_mode()