Description of problem:

Using mkksiso to build a custom ISO fails with error "Invalid APM signature"


Version-Release number of selected component (if applicable): lorax-34.12-1.fc34


How reproducible: Always


Steps to Reproduce:
1. Download official ISO from distribution of preference. (for example Fedora-Everything-netinst-x86_64-34-1.2.iso) 
2. Point mkksiso to use the ISO from the official distro you have downloaded 
3. Observe error in output

Actual results:

sudo mkksiso /share/fedora_stable/fedora_stable_kickstart.cfg ~/Downloads/Fedora-Everything-netinst-x86_64-34-1.2.iso ~/Documents/fedora-fantasy-stable.iso
[sudo] password for angelotheo: 
INFO:Running... mount -o loop /home/angelotheo/Downloads/Fedora-Everything-netinst-x86_64-34-1.2.iso /tmp/lorax.imgutils.mzr_f9eh
INFO:mount: /tmp/lorax.imgutils.mzr_f9eh: WARNING: source write-protected, mounted read-only.
ERROR:Problem reading label from /home/angelotheo/Downloads/Fedora-Everything-netinst-x86_64-34-1.2.iso: Invalid APM signature
INFO:Volume Id = None
INFO:Using xorrisofs to create the new iso
INFO:Running... umount /tmp/lorax.imgutils.mzr_f9eh
Traceback (most recent call last):
  File "/usr/sbin/mkksiso", line 618, in <module>
    main()
  File "/usr/sbin/mkksiso", line 613, in main
    app.run()
  File "/usr/sbin/mkksiso", line 560, in run
    self.edit_configs(self.iso.mount_dir, tmpdir)
  File "/usr/sbin/mkksiso", line 456, in edit_configs
    self._edit_isolinux(isodir, tmpdir)
  File "/usr/sbin/mkksiso", line 472, in _edit_isolinux
    escaped_iso_label = udev_escape(self.iso.label)
  File "/usr/lib/python3.9/site-packages/pylorax/treebuilder.py", line 421, in udev_escape
    for ch in label:
TypeError: 'NoneType' object is not iterable



Expected results:

Custom ISO to be built as expected. It's worth noting that this works as expected under Fedora 33 or if manually installing lorax f33 and it's dependencies on Fedora 34.