The line art modifier added a wmNotifier in it's
GpencilModifierTypeInfo.generateStrokes callback which isn't thread-safe
when called from the depsgraph. This was from the original inclusion
of the feature [0] however a more recent optimization to notifier
lookups [1] made the crash occur more frequently.
Remove the notifier as modifiers should not be adding WM level events
and it works without it.
[0]: 3e87d8a431
[1]: 0aaff9a07d
2907227db2