Change command disconnect

Update the disconnect command so that it doesn't say disconnected when it doesn't have an active player in the guild. Additionally adds i18n support.

Update cmd-restart-invalid-arg i18n to match with what's in the code.

config/i18n/en.json

@@ -140,12 +140,14 @@
     "cmd-move-indexes-not-intergers": "Song indexes must be integers.",
     "cmd-move-invalid-indexes": "Sent indexes are outside of playlist scope!",
     "cmd-move-success": "Successfully moved the requested song from position number {} in queue to position {}!",
-    "cmd-restart-invalid-arg": "Invalid option given, use soft or full.",
+    "cmd-restart-invalid-arg": "Invalid option given, use: soft, full, upgrade, uppip, or upgit.",
     "cmd-restart-soft": "{emoji} Restarting current instance...",
     "cmd-restart-full": "{emoji} Restarting bot process...",
     "cmd-restart-uppip": "{emoji} Will try to upgrade required pip packages and restart the bot...",
     "cmd-restart-upgit": "{emoji} Will try to update bot code with git and restart the bot...",
     "cmd-restart-upgrade": "{emoji} Will try to upgrade everything and restart the bot...",
+    "cmd-disconnect-success": "Disconnected from `{0.name}",
+    "cmd-disconnect-no-voice":  "Not currently connected to `{0.name}`",
     "playlists-noperms": "You are not allowed to request playlists",
     "playlists-big": "Playlist has too many entries ({0} > {1})",
     "playlists-limit": "Playlist entries + your already queued songs reached limit ({0} + {1} > {2})",

musicbot/bot.py

@@ -4525,8 +4525,22 @@ async def cmd_disconnect(self, guild):
 
         Forces the bot leave the current voice channel.
         """
-        await self.disconnect_voice_client(guild)
-        return Response("Disconnected from `{0.name}`".format(guild), delete_after=20)
+        voice_client = self.get_player_in(guild)
+        if voice_client:
+            await self.disconnect_voice_client(guild)
+            return Response(
+                self.str.get(
+                    "cmd-disconnect-success", "Disconnected from `{0.name}`"
+                ).format(guild),
+                delete_after=20,
+            )
+        else:
+            raise exceptions.CommandError(
+                self.str.get(
+                    "cmd-disconnect-no-voice", "Not currently connected to `{0.name}`"
+                ).format(guild),
+                expire_in=30,
+            )
 
     async def cmd_restart(self, _player, channel, leftover_args, opt="soft"):
         """
@@ -4545,7 +4559,7 @@ async def cmd_restart(self, _player, channel, leftover_args, opt="soft"):
             raise exceptions.CommandError(
                 self.str.get(
                     "cmd-restart-invalid-arg",
-                    "Invalid option given, use: soft, full, upgrade, uppip, or upgit",
+                    "Invalid option given, use: soft, full, upgrade, uppip, or upgit.",
                 ),
                 expire_in=30,
             )