Return member objects for users that are not actually members

Most of the data in the objects will be empty, but at least a valid matrix id is provided.
This fixes missing data in some places in the UI (e.g., in HiddenDelegate)

src/timeline/models/messagemodel.cpp

@@ -154,10 +154,6 @@ QVariant MessageModel::data(const QModelIndex &idx, int role) const
             mId = event.value().get().senderId();
         }
 
-        if (!m_room->isMember(mId)) {
-            return QVariant::fromValue<NeochatRoomMember *>(emptyNeochatRoomMember);
-        }
-
         return QVariant::fromValue<NeochatRoomMember *>(m_room->qmlSafeMember(mId));
     }