make update_channel more flexible against non-guild chans

..to handle gdm edits

litecord/blueprints/channels.py

@@ -411,25 +411,39 @@ async def update_channel(channel_id):
     user_id = await token_check()
     ctype, guild_id = await channel_check(user_id, channel_id)
 
-    if ctype not in GUILD_CHANS:
-        raise ChannelNotFound('Can not edit non-guild channels.')
+    if ctype not in (ChannelType.GUILD_TEXT, ChannelType.GUILD_VOICE,
+                     ChannelType.GROUP_DM):
+        raise ChannelNotFound('unable to edit unsupported chan type')
 
+    is_guild = ctype in GUILD_CHANS
+
+    if is_guild:
         await channel_perm_check(user_id, channel_id, 'manage_channels')
-    j = validate(await request.get_json(), CHAN_UPDATE)
 
-    # TODO: categories?
+    j = validate(await request.get_json(),
+                 CHAN_UPDATE if is_guild else GROUP_DM_UPDATE)
+
+    # TODO: categories
     update_handler = {
         ChannelType.GUILD_TEXT: _update_text_channel,
         ChannelType.GUILD_VOICE: _update_voice_channel,
+        # ChannelType.GROUP_DM: _update_group_dm,
     }[ctype]
 
+    if is_guild:
         await _update_channel_common(channel_id, guild_id, j)
+
     await update_handler(channel_id, j)
 
     chan = await app.storage.get_channel(channel_id)
 
+    if is_guild:
+        await app.dispatcher.dispatch(
+            'guild', guild_id, 'CHANNEL_UPDATE', chan)
+    else:
+        await app.dispatcher.dispatch(
+            'channel', channel_id, 'CHANNEL_UPDATE', chan)
 
-    await app.dispatcher.dispatch('guild', guild_id, 'CHANNEL_UPDATE', chan)
     return jsonify(chan)