When the subtype of a custom property is set programmatically to
something that isn't in the subtype enum of this operator, attempting
to edit it will throw an error. This check should avoid that, by simply
not setting the subtype if it's not in the enum, resulting in a default
subtype of NONE. This is the second attempt at #112582, which I broke
when messing with branches.
Pull Request: https://projects.blender.org/blender/blender/pulls/114003
2e084addb5