Space overview: Fix displayed name of direct chats

When in the space overview page, direct chats were previously only
shown with their room ID. Fix this by getting the actual NeoChatRoom
and its displayName.

src/spaces/models/spacechildrenmodel.cpp

@@ -173,6 +173,10 @@ QVariant SpaceChildrenModel::data(const QModelIndex &index, int role) const
 
     SpaceTreeItem *child = getItem(index);
     if (role == DisplayNameRole) {
+        if (const auto room = static_cast<NeoChatRoom *>(m_space->connection()->room(child->id()))) {
+            return room->displayName();
+        }
+
         auto displayName = child->name();
         if (!displayName.isEmpty()) {
             return displayName;