Fix avatar URLs for rooms

Room avatar URLs don't specify the new mxc:// format the user avatars
use, so we need to carve out a workaround for them.

src/models/completionmodel.cpp

@@ -87,7 +87,7 @@ QVariant CompletionModel::data(const QModelIndex &index, int role) const
             return m_filterModel->data(filterIndex, RoomListModel::CanonicalAliasRole);
         }
         if (role == IconNameRole) {
-            return m_filterModel->data(filterIndex, RoomListModel::AvatarRole);
+            return QStringLiteral("image://mxc//%1").arg(m_filterModel->data(filterIndex, RoomListModel::AvatarRole).toString());
         }
     }
     if (m_autoCompletionType == Emoji) {