Bulk edit of Interfaces of VMs without cluster fails

[larsux]

NetBox version

v3.6.5

Python version

3.8

Steps to Reproduce

1. Create VM and assign only a Site, not a Cluster
2. Create Interface for VM
3. Mark Interface and click on "Edit Selected"

Expected Behavior

Edit form for selected VM Interface(s) appear

Observed Behavior

Exception Window with the following Content:

<class 'AttributeError'>

'NoneType' object has no attribute 'site'

Python version: 3.8.10
NetBox version: 3.6.5
Plugins: 
  netbox_demo: 0.3.1

When generating the bulk edit form, the site is extracted from the cluster of the virtual machine, which fails if no cluster is assigned to the VM:

  File "/opt/netbox/netbox/virtualization/forms/bulk_edit.py", line 272, in __init__
     site = interface.virtual_machine.cluster.site
AttributeError: 'NoneType' object has no attribute 'site'