fdo#81182: glTF window size does not match with the scene size after resizing

When viewport changed it is necessary to resize the whole scene.
Calling releasFbo removes size dependent objects and triggers
creating the new ones with the new size.

Change-Id: Ibd8be1e92be92da31add4a30aa799f0995b1cc88
(cherry picked from commit 3cd7c0f6b6cdb8ebc6c72d2ffe1e0bc18968e27b)
Reviewed-on: https://gerrit.libreoffice.org/10352
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>