installer crash when no partition on main disk

[eroussy]

When launching the installer on a machine with a disk with no partition, the installer crashes.

Step to reproduce

• Clear all partitions on disk of the machine sudo wipefs -a <disk_path>
• Reboot on the seapath-installer USB key
• The installer crashes
• Open a terminal and launch sudo calamares -d to see a a Segmentation fault

Work-around

• Boot on the seapath-installer USB key
• Open a terminal
• Create a dummy file system on your disk `sudo mkfs.ext4 <disk_path>
• Relaunch calamares manually sudo calamares

[Paullgk]

Fixed with #9