Description of problem:
If a user with an existing Mageia system installed in UEFI mode accidentally boots the install media in PC-BIOS mode to do an upgrade, then the upgrade will continue without warning.
This is an easy mistake especially when an inserted bootable disk is launched automatically on power-up.
It would be good if the installer could detect and warn/advise about this situation before continuing with the upgrade.
Version-Release number of selected component (if applicable):
Steps to Reproduce: