Image center (principal point) potentially not set correctly when loading a new project

Steps to reproduce:

1. Open markerCasern test example
2. Open multiColorMarkerWithAruco_dictMip36h12 test example

Problem: center is not read correctly

Excerpt from pet-file:

<INTRINSIC_PARAMETERS [..] CX="2380.0599999999999" CY="1911.8699999999999" [...]/>

Could reproduce on commit 7637410538207f2cb6df0e33a3e4fb033ca3c280, i.e. before the extraction of the IntrinsicBox