Description of problem:
Steps to reproduce:

1. Start installation on PPC64, where there's already a partitioning layout from previous installation
2. In partitioning step, remove /, /boot and swap partition
3. In unknown "tab", remove PPC PReP partition (there's probably a bug, because the space is marked as Unknown, not removed
4. Let anaconda create the partitioning for you (There's a link for it)
5. Anaconda doesn't create a PReP partition, so create it manually:
6. First resize the /boot partition (500MB -> 495MB)
7. After this step anaconda crashes.


Version-Release number of selected component:
anaconda-18.11

Additional info:
libreport version: 2.0.14
cmdline:        /usr/bin/python  /sbin/anaconda
kernel:         3.6.0-0.27.el7.ppc64

description:
:The following was filed automatically by anaconda:
:anaconda 18.11 exception report
:Traceback (most recent call first):
:  File "/usr/lib64/python2.7/site-packages/pyanaconda/storage/devicetree.py", line 385, in _removeDevice
:    "Logical partitions present." % dev.name)
:  File "/usr/lib64/python2.7/site-packages/pyanaconda/storage/devicetree.py", line 425, in registerAction
:    self._removeDevice(action.device)
:  File "/usr/lib64/python2.7/site-packages/pyanaconda/storage/__init__.py", line 1219, in destroyDevice
:    self.devicetree.registerAction(action)
:  File "/usr/lib64/python2.7/site-packages/pyanaconda/storage/partitioning.py", line 692, in updateExtendedPartitions
:    storage.destroyDevice(part)
:  File "/usr/lib64/python2.7/site-packages/pyanaconda/storage/partitioning.py", line 790, in doPartitioning
:    updateExtendedPartitions(storage, disks)
:  File "/usr/lib64/python2.7/site-packages/pyanaconda/storage/__init__.py", line 1913, in allocatePartitions
:    doPartitioning(self)
:  File "/usr/lib64/python2.7/site-packages/pyanaconda/storage/__init__.py", line 3198, in post_create
:    self.storage.allocatePartitions()
:  File "/usr/lib64/python2.7/site-packages/pyanaconda/storage/__init__.py", line 2086, in newDevice
:    factory.post_create()
:  File "/usr/lib64/python2.7/site-packages/pyanaconda/ui/gui/spokes/custom.py", line 974, in _save_right_side
:    raid_level=raid_level)
:  File "/usr/lib64/python2.7/site-packages/pyanaconda/ui/gui/spokes/custom.py", line 1534, in on_selector_clicked
:    self._save_right_side(self._current_selector)
:  File "/usr/lib64/python2.7/site-packages/pyanaconda/ui/gui/spokes/lib/accordion.py", line 188, in _onSelectorClicked
:    cb(selector)
:ValueError: Cannot remove extended partition sda4.  Logical partitions present.