Handle case where PRESENCE_UPDATE adds members to cache.

When we don't request offline members, members that are going from
offline to online in the server will become available via the
PRESENCE_UPDATE event. This should be transparent to the user since
technically the member exists in the server and thus on_member_update
is used instead of on_member_join.

discord/state.py

@@ -134,12 +134,19 @@ class ConnectionState:
 
     def parse_presence_update(self, data):
         server = self._get_server(data.get('guild_id'))
-        if server is not None:
+        if server is None:
+            return
+
         status = data.get('status')
         user = data['user']
         member_id = user['id']
         member = server.get_member(member_id)
-            if member is not None:
+        if member is None:
+            # if the member is not in cache then it's being "lazily"
+            # loaded due to large_threshold so we need to add it into
+            # the cache and then update that instead.
+            member = self._add_member(server, data)
+
         old_member = copy.copy(member)
         member.status = data.get('status')
         try:
@@ -192,9 +199,7 @@ class ConnectionState:
 
         self.dispatch('channel_create', channel)
 
-    def parse_guild_member_add(self, data):
-        server = self._get_server(data.get('guild_id'))
-
+    def _add_member(self, server, data):
         roles = [server.default_role]
         for roleid in data.get('roles', []):
             role = utils.get(server.roles, id=roleid)
@@ -204,6 +209,11 @@ class ConnectionState:
         data['roles'] = roles
         member = Member(server=server, **data)
         server._add_member(member)
+        return member
+
+    def parse_guild_member_add(self, data):
+        server = self._get_server(data.get('guild_id'))
+        self._add_member(server, data)
         server._member_count += 1
         self.dispatch('member_join', member)